Harq signaling for grant-free uplink transmissions

ABSTRACT

In a wireless communication system, a grant-free uplink transmission is an uplink transmission sent from a user equipment (UE) to a base station that does not need a dynamic and explicit scheduling grant from the base station. Systems and methods are disclosed for performing hybrid automatic repeat request (HARQ) for grant-free uplink transmissions. Signaling relating to the ACK/NACK for the HARQ, as well as signaling relating to configuring the UE for grant-free uplink transmission, is also disclosed.

PRIORITY

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 62/416,939 titled “HARQ Systems and Methods forGrant-Free Uplink Transmissions” filed Nov. 3, 2016, and to U.S.Provisional Patent Application Ser. No. 62/421,087 titled “HARQ Systemsand Methods for Grant-Free Uplink Transmissions” filed Nov. 11, 2016,and to U.S. Provisional Patent Application Ser. No. 62/459,949 titled“HARQ Signaling for Grant-Free Uplink Transmissions” filed Feb. 16,2017, all three of which are incorporated herein by reference.

FIELD

The present application relates to grant-free uplink transmissions.

BACKGROUND

In some wireless communication systems, a user equipment (UE) wirelesslycommunicates with a base station to send data to the base station and/orreceive data from the base station. A wireless communication from a UEto a base station is referred to as an uplink communication. A wirelesscommunication from a base station to a UE is referred to as a downlinkcommunication.

Resources are required to perform uplink and downlink communications.For example, a UE may wirelessly transmit data to a base station in anuplink transmission at a particular frequency and/or during a particularslot in time. The frequency and time slot used are examples ofresources.

Some wireless communication systems may support grant-based uplinktransmissions. That is, if a UE wants to transmit data to a basestation, the UE requests uplink resources from the base station. Thebase station grants the uplink resources, and then the UE sends theuplink transmission using the granted uplink resources. An example ofuplink resources that may be granted by the base station is a set oftime-frequency locations in an uplink orthogonal frequency-divisionmultiple access (OFDMA) frame.

Some wireless communication systems may also or instead supportgrant-free uplink transmissions. That is, a UE may send uplinktransmissions using certain uplink resources possibly shared with otherUEs, without specifically requesting use of the resources and withoutspecifically being granted the resources by the base station. Agrant-free uplink transmission does not need a dynamic and explicitscheduling grant from the base station.

In some cases, when a UE sends a grant-free uplink transmission, thebase station may not be able to decode the data in the uplinktransmission.

SUMMARY

Hybrid automatic repeat request (HARQ) is a method in which data to betransmitted is encoded using an error correction code. Then, if theencoded data is corrupted during transmission and the receiver is unableto correct the errors, automatic repeat request (ARQ) is performed.

The HARQ signaling for grant-based uplink transmissions may not beavailable for grant-free uplink transmissions because grant-free uplinktransmissions do not receive an explicit scheduling grant from the basestation.

Systems and methods are disclosed herein for performing HARQ forgrant-free uplink transmissions. Signaling relating to the ACK/NACK forthe HARQ, as well as signaling relating to configuring a UE forgrant-free uplink transmission, is also disclosed.

By using the systems and methods described herein, HARQ signaling forgrant-free uplink transmissions may therefore be provided. Inparticular, some embodiments below provide support for ACK/NACK feedbackfor grant-free transmissions and retransmissions.

In one embodiment, there is provided a method performed by a basestation. The method includes the base station receiving a firstgrant-free uplink transmission from a first UE. The method furtherincludes the base station receiving a second grant-free uplinktransmission from a second UE. The method further includes transmitting,to the first UE and to the second UE, a group ACK/NACK messageindicating an ACK or a NACK corresponding to the first grant-free uplinktransmission and an ACK or a NACK corresponding to the second grant-freeuplink transmission. A base station configured to perform the method isalso disclosed.

In another embodiment there is provided a method performed by a firstUE. The method includes transmitting a first grant-free uplinktransmission to a base station. The method further includes receiving agroup ACK/NACK message indicating an ACK or a NACK corresponding to thefirst grant-free uplink transmission and an ACK or a NACK correspondingto a second grant-free uplink transmission from a second UE. A UE toperform the method is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described, by way of example only, with reference tothe accompanying figures wherein:

FIG. 1 is a block diagram of a base station and a plurality of UEs,according to one embodiment;

FIG. 2 is a block diagram showing a base station and UE in more detail,according to one embodiment;

FIG. 3 illustrates example formats for a grant-free uplink transmission;

FIGS. 4 and 5 illustrate tables showing example mappings betweentransmissions and MA signatures or physical resources;

FIG. 6 is a method performed by a base station, according to oneembodiment;

FIG. 7 illustrates an example mapping between MA signature/grant-freeaccess region and orthogonal sequence/time-frequency location offeedback;

FIG. 8 is a method performed by a UE and base station, according to oneembodiment;

FIG. 9 is a method performed by a UE and base station, according toanother embodiment;

FIGS. 10 to 13 illustrate examples of group ACK/NACKs;

FIG. 14 is a method performed by a UE and base station, according toanother embodiment;

FIG. 15 is a method performed by two UEs and a base station, accordingto one embodiment;

FIG. 16 is a time-frequency resource partition showing a groupacknowledgement for packets sent during five previous time slots;

FIG. 17 is a method performed by a UE and base station, according toanother embodiment;

FIG. 18 is a method performed by a UE and base station, according toanother embodiment; and

FIG. 19 is a method performed by a UE, according to one embodiment.

DETAILED DESCRIPTION

For illustrative purposes, specific example embodiments will now beexplained in greater detail below in conjunction with the figures.

FIG. 1 is a block diagram of a base station 100 and a plurality of UEs102 a-c, according to one embodiment.

The word “base station” encompasses any device that wirelessly receivesdata in the uplink from UEs. Therefore, in some implementations, thebase station 100 may be called other names, such as a transmit andreceive point (TRP), a base transceiver station, a radio base station, anetwork node, a transmit/receive node, a Node B, an eNodeB (eNB), a gNB(sometimes called a “gigabit” Node B), a relay station, or a remoteradio head. Also, in some embodiments, the parts of the base station 100may be distributed. For example, some of the modules of the base station100 may be located remote from the equipment housing the antennas of thebase station 100, and may be coupled to the equipment housing theantennas over a communication link (not shown). Therefore, in someembodiments, the term base station 100 may also refer to modules on thenetwork side that perform processing operations (e.g. decoding andmessage generation) that are not necessarily part of the equipmenthousing the antennas of the base station 100. The modules may also becoupled to other base stations.

In operation, UEs 102 a-c may each send grant-free uplink transmissionsto the base station 100. A grant-free uplink transmission is an uplinktransmission that is sent using uplink resources not specificallygranted to the UE by the base station 100. A grant-free uplinktransmission does not need a dynamic and explicit scheduling grant fromthe base station 100.

Grant-free uplink transmissions are sometimes called “grant-less”,“schedule free”, or “schedule-less” transmissions, or transmissionswithout grant. Grant-free uplink transmissions from different UEs 102a-c may be transmitted using the same designated resources, in whichcase the grant-free uplink transmissions are contention-basedtransmissions. Grant-free uplink transmissions may be suitable fortransmitting bursty traffic with short packets from the UEs 102 a-c tothe base station 100, and/or for transmitting data to the base station100 in real-time or with low-latency. Examples of applications in whicha grant-free uplink transmission scheme may be utilized include: massivemachine type communication (m-MTC), ultra-reliable low latencycommunications (URLLC), smart electric meters, teleprotection in smartgrids, and autonomous driving. However, grant-free uplink transmissionschemes are not limited to these applications.

The uplink resources on which grant-free transmissions are sent will bereferred to as “grant-free uplink resources”. For example, thegrant-free uplink resources may be a designated region in an OFDMAframe. The UEs 102 a-c may use the designated region to send theirgrant-free uplink transmissions, but the base station 100 does not knowwhich of the UEs 102 a-c, if any, are going to send a grant-free uplinktransmission in the designated region.

The grant-free uplink resources may be predefined, e.g. known in advanceto both the UEs and the base station 100. The grant-free uplinkresources may be static (never change), or the grant-free uplinkresources may be configured semi-statically. A semi-static configurationmeans it is configured once and can only be updated/changed slowly, suchas once in many frames or may only be updated as needed. A semi-staticchange differs from a dynamic change in that a semi-static change doesnot occur as often as a dynamic change. For example, a dynamicchange/update may refer to a change every subframe or every fewsubframes, and a semi-static change may refer to a change that onlyoccurs once every several OFDM frames, once every few seconds, or updateonly if needed.

In some embodiments, the grant-free uplink resources may bepreconfigured, e.g. there may be a plurality of possible predefinedgrant-free uplink resource partitions, and the base station 100 or thenetwork may semi-statically pick one of the predefined grant-free uplinkresource partitions and signal to the UEs the grant-free uplink resourcepartition being used. In some embodiments, the base station 100 and/orthe UEs may be configured during their manufacture to know which uplinkresources to use as grant-free uplink resources, e.g. through predefinedtables loaded during manufacture. In some embodiments, the grant-freeuplink resources may be semi-statically configured, e.g. by using acombination of broadcast signalling, higher layer signalling (RRCsignalling) and dynamic signalling (e.g. DCI) by the base station 100.By dynamically signaling the grant-free uplink resources, the basestation 100 or network may adapt to the system traffic load of the UEs.For example, more grant-free uplink resources may be allocated whenthere are more UEs being served that may send grant-free uplinktransmissions. In some embodiments, a control node (e.g. a computer) inthe network may determine the grant-free uplink resources to be used.The network may then indicate the grant-free uplink resources to thebase station and the UEs. In some embodiments, a UE operating ingrant-free mode may be semi-statically configured to combine: 1) the RRCsignaling information and the system information; or 2) the RRCsignaling information and the DCI information; or 3) the RRC signalinginformation, the system information and the DCI information to determinean assigned transmission resource.

FIG. 1 illustrates a message 150 being sent by UE 102 a in a grant-freeuplink transmission over uplink channel 156. The message 150 istransmitted using a multiple access (MA) resource. A MA resource iscomprised of a MA physical resource (e.g. a time-frequency block) and atleast one MA signature. The MA signature may include (but is not limitedto) at least one of the following: a codebook/codeword, a sequence, aninterleaver and/or mapping pattern, a pilot, a demodulation referencesignal (e.g. a reference signal for channel estimation), a preamble, aspatial-dimension, and a power-dimension. The term “pilot” refers to asignal that at least includes a reference signal, e.g. a demodulationreference signal. The reference signal may be the MA signature. In someembodiments, the pilot may include the demodulation reference signal,possibly along with a channel-estimation-oriented preamble, or a randomaccess channel (LTE-like RACH) preamble.

In some embodiments, the uplink transmissions may use non-orthogonalmultiple access (NOMA), such as: sparse code multiple access (SCMA),interleave-grid multiple access (IGMA), multi-user shared access (MUSA),low code rate spreading, frequency domain spreading, non-orthogonalcoded multiple access (NCMA), pattern division multiple access (PDMA),resource spread multiple access (RSMA), low density spreading withsignature vector extension (LDS-SVE), low code rate and signature basedshared access (LSSA), non-orthogonal coded access (NOCA), interleavedivision multiple access (IDMA), repetition division multiple access(RDMA), or group orthogonal coded access (GOCA). Depending upon themultiple access method used, the MA signature may take different forms.The MA signature may relate to the specific format used for the multipleaccess method. For example, if SCMA is used, then the MA signature forthe uplink transmission may be the SCMA codebook used for the uplinktransmission. As another example, if IGMA is used, then the MA signaturefor the uplink transmission may be the IGMA's signature, interleavingpattern or grid mapping used for the uplink transmission.

FIG. 2 is a block diagram showing the base station 100 and UE 102 a ofFIG. 1 in more detail. The base station 100 includes a grant-freetransmission module 104 for processing grant-free transmissions receivedfrom UEs 102 a-c and for participating in the HARQ methods describedherein relating to the received grant-free transmissions. For example,the grant-free transmission module 104 may include a grant-freetransmission decoder 206. The base station further includes an encoder210 for encoding information, such as downlink control information(DCI), destined for the UEs 102 a-c. The base station 100 also includesa receiver 209 for receiving uplink transmissions from the UEs 102 a-c,and a transmitter 211 for sending messages to the UEs 102 a-c in thedownlink. One or more antennas are coupled to the receiver 209 andtransmitter 211. Only one antenna 208 is illustrated. The base station100 further includes memory 204. The base station 100 further includesother components for operation, e.g. to implement the physical layer,but these have been omitted for the sake of clarity.

The grant-free transmission module 104 and its components (e.g. thegrant-free transmission decoder 206), as well as the encoder 210 andprocessing components of the receiver 209 and transmitter 211, may beimplemented by one or more processors that execute instructions thatcause the one or more processors to perform the operations of theencoder 210, the receiver 209, the transmitter 211, and the grant-freetransmission module 104 and its components. Alternatively, the encoder210, the receiver 209, the transmitter 211, and the grant-freetransmission module 104 and its components may be implemented usingdedicated integrated circuitry, such as an application specificintegrated circuit (ASIC), a graphics processing unit (GPU), or aprogrammed field programmable gate array (FPGA) for performing theoperations of the encoder 210, the receiver 209, the transmitter 211,and the grant-free transmission module 104 and its components.

The UE 102 a also includes a complementary grant-free transmissionmodule 106 for generating and sending grant-free messages and forparticipating in the HARQ methods described herein related to thegrant-free messages. For example, the grant-free transmission module 106includes a grant-free message generator 214 for generating messages tobe transmitted in grant-free uplink transmissions. Generating agrant-free message may include encoding, in encoder 219, the data to betransmitted in the message, and modulating the encoded data. The UE 102a further includes a decoder 218 for decoding information from the basestation 100, e.g. for decoding DCI that was encoded by encoder 210. TheUE 102 a further includes a transmitter 215 for transmitting uplinktransmissions and a receiver 217 for receiving messages from the basestation 100 in the downlink. One or more antennas are coupled to thetransmitter 215 and the receiver 217. Only one antenna 216 isillustrated. The UE 102 a further includes memory 212. The UE 102 afurther includes other components for operation, e.g. to implement thephysical layer, but these have been omitted for the sake of clarity.

The grant-free transmission module 106 and its components (e.g. thegrant-free message generator 214), as well as the decoder 218 andprocessing components of the transmitter 215 and the receiver 217, maybe implemented by one or more processors that execute instructions thatcause the one or more processors to perform the operations of thedecoder 218, the transmitter 215, the receiver 217, and the grant-freetransmission module 106 and its components. Alternatively, the decoder218, the transmitter 215, the receiver 217, and the grant-freetransmission module 106 and its components may be implemented usingdedicated integrated circuitry, such as an ASIC, GPU, or a programmedFPGA for performing the operations of the decoder 218, the transmitter215, the receiver 217, and the grant-free transmission module 106 andits components.

Example Message Formats for Grant-Free Uplink Transmissions

FIG. 3 illustrates example formats for the message 150 sent by UE 102 ain the grant-free uplink transmission of FIG. 1. The example formats areshown in stippled bubble 124.

In example 126, the message 150 includes a MA signature 152, as well asdata 154 and a UE ID 156. The UE ID 156 is information used by the basestation 100 to identify the UE. In example 126, the data 154 and the UEID 156 are encoded together, and a corresponding cyclic redundancy check(CRC) 158 is generated and included in the message 150. In someembodiments, the UE ID 156 is instead embedded (e.g. scrambled) in theCRC 158, which may reduce the payload size. If the UE ID 156 is embeddedin the CRC 158, then the base station 100 needs to know the UE ID orperform blind detection using all potential UE ID's in order to decodethe CRC 158.

Example 128 is a variation of example 126 in which the UE ID 156 isseparately encoded from the data 154. Therefore, a separate CRC 160 isassociated with the UE ID 156. In some embodiments, the UE ID 156 may beinside one or more other headers, in which case the CRC 160 is for theheaders in which the CRC 160 is located. In example 128, the UE ID 156may be transmitted with a lower modulation and coding scheme (MCS) thanthe data 154 in order to facilitate decoding of the UE ID 156. There maybe situations in which the UE ID 156 is successfully decoded, but thedata 154 is not successfully decoded.

In examples 126 and 128, the MA signature 152 is illustrated asoccupying separate time-frequency resources from the data 154, e.g. atthe start of the message 150. This may be the case if, for example, theMA signature 152 consists of a reference signal and/or a preamble.However, the MA signature 152 may instead be part of the transmissionscheme itself, e.g. the codebook used or the mapping or interleavingpattern used, in which case the MA signature 152 would not occupyseparate time-frequency resources from the data 154. Also, inembodiments in which the MA signature 152 does occupy separatetime-frequency resources from the data 154, the resources do notnecessarily have to be at the start of the message 150.

Example 130 in FIG. 1 shows a variation in which the UE ID 156 and thedata 154 are transmitted through different resources. For example, theUE ID 156 may be transmitted as part of a control channel, such as aphysical uplink control channel (PUCCH). The data 154 may be transmittedin a grant-free region of an uplink data channel. The MA signature isnot illustrated in example 130, but the MA signature would be part ofthe data transmission.

In some other embodiments, the UE ID is not explicitly transmitted. Forexample, in some URLLC scenarios, based on the resource and referencesignal configuration, detecting the reference signal along with theinformation about the grant-free resources may be enough to identify theUE. In this case, the UE ID does not need to be explicitly transmitted,and the base station can identify the UE after successfully detectingthe reference signal. An example is shown at 132. Only the MA signature152 and the data 154 are included in the message, not a UE ID. The UE IDcan be determined based on the MA signature 152 and the grant-freeuplink resources used to send the message.

When the UE sends message 150 to the base station 100, the base station100 first attempts to detect the MA signature. MA signature detectionmay involve a blind detection process in which the MA signature isdetected among all of the possible choices of MA signatures. Detectingthe MA signature is referred to as activity detection. As an example,the MA signature in the grant-free uplink transmission may be areference signal, and activity detection by the base station wouldtherefore comprise detecting the reference signal in the grant-freeuplink transmission. As another example, the MA signature in thegrant-free uplink transmission may be a combination of the referencesignal and the codebook or signature used by the UE in the grant-freeuplink transmission, and activity detection by the base station wouldtherefore comprise detecting the combination of the reference signal andcodebook/signature used in the grant-free uplink transmission.

By successfully performing activity detection, the base station 100knows that a UE has sent a grant-free uplink transmission. However,successful activity detection may or may not reveal the identity of theUE to the base station 100. If there is a unique mapping between a UEand an MA signature (e.g. for a given MA physical resource each UE hasbeen assigned to use a different MA signature), then successful activitydetection reveals the identity of the UE that sent the grant-free uplinktransmission. Otherwise, in general, successful activity detection doesnot reveal the identity of the UE that sent the grant-free uplinktransmission, although it may reveal that the UE is from a particulargroup of UEs, if different groups of UEs are assigned different MAsignatures. In some embodiments, activity detection may further includeobtaining the UE ID, e.g. if the UE ID is encoded separately from thedata 154, as in example message 128.

After activity detection is successful, the base station 100 thenattempts to perform channel estimation based on the MA signature andoptionally additional reference signals multiplexed with the datamessage, and then decode the data 154. If data decoding is alsosuccessful, then the base station 100 can send an acknowledgement (ACK)to the UE in the downlink indicating that the base station 100 hassuccessfully decoded the data 154. In embodiments in which successfulactivity detection does not reveal the identity of the UE, thensuccessful decoding of the rest of the message 150 will reveal theidentity of the UE, in which case the base station 100 will know the UEto which to send the ACK. If data decoding is not successful, then anegative acknowledgement (NACK) may be sent by the base station,possibly with a grant for a retransmission. As discussed in more detaillater, in some embodiments a NACK is not sent if decoding of the datawas unsuccessful. As also discussed in more detail later, in someembodiments, if a NACK is sent, the NACK may not necessarily includeinformation that can uniquely identify the UE to which the NACK is beingsent because the base station may not be able to uniquely identify theUE.

In one example, the MA signature 152 in example 126 is a referencesignal. The base station 100 may first successfully perform activitydetection by successfully decoding the reference signal sequence. Thereference signal sequence may then be used by the base station 100 forchannel estimation of the uplink channel 156. To facilitate successfuldecoding of the reference signal, the reference signal may betransmitted with a low MCS. Once the reference signal is successfullydecoded and channel estimation performed, the base station 100 thendecodes the payload having the data 154 and UE ID 156. The base station100 can then read the UE ID 156 to be informed of which UE thegrant-free transmission came from. The base station 100 can then send anACK to the UE in the downlink indicating that the base station 100 hassuccessfully decoded the data 154.

UE Identification by the Base Station

The grant-free uplink transmission may include a UE ID, e.g. UE ID 156in FIG. 3. The UE ID is information used by the base station 100 toidentify the UE.

In some embodiments, the UE ID may be a radio network temporaryidentifier (RNTI), or may be based on a RNTI.

In some embodiments, the UE ID may be an index. The index distinguishesthe UE from other UEs that are also permitted to send grant-free uplinktransmissions on the same grant-free uplink resources. For example, theindex may distinguish the UE from other UEs that are also permitted tosend grant-free uplink transmissions on a shared time-frequency regionin the same time slot, transmission time interval (TTI), or subframe.

In some embodiments, the UE ID does not need to be identical or fixedacross one cell or serving area. For example, if a particular UE is partof a group of ten UEs allowed to send grant-free uplink transmissions inuplink resource partition A, then the UE ID may be an index between 1and 10, which distinguishes the UE from the other nine UEs in the group.The base station 100 uses the index and knowledge of which grant-freeuplink resource partition was used to determine which particular UE sentthe grant-free uplink transmission.

In some embodiments, for a given MA physical resource, the UEs usingthat MA physical resource for grant-free uplink transmissions areassigned different MA signatures. The base station 100 may then uniquelyidentify the UE that sent the grant-free uplink transmission based onthe combination of the MA signature and the MA physical resource used.

In some embodiments, for a given MA physical resource, some of the UEsusing that MA physical resource for grant-free uplink transmissions mayuse the same MA signature. A UE index may be assigned by the basestation 100 to differentiate between UEs that use the same MA signature.For example, if two UEs both use the same MA signature, then one of theUEs may be assigned UE index “1” as their UE ID, and the other UE may beassigned UE index “2” as their UE ID. The indices “1” and “2” may bereused for other UEs sharing a same MA signature. Then, the base station100 uses the combination of the MA physical resource, the MA signature,and the UE index to identify the UE that sent the grant-free uplinktransmission.

In some embodiments, each UE may be assigned the use of a different MAsignature that is known by the base station 100 and the UE. Theassignment may change over time. For example, a UE may be assigned afirst MA signature, and then at a later time the UE may be assignedanother MA signature. The MA signature received and the time-frequencyresource used may uniquely identify the UE.

In some embodiments, a particular UE may be assigned multiple MAsignatures, e.g. a first MA signature for initial transmissions and asecond MA signature for retransmissions. In some embodiments, the MAsignature assigned to each UE of a group of UEs may change over timeaccording to a hopping pattern. In some embodiments, the assignment ofMA signatures to UEs may be reused or repeated for different UEs indifferent grant-free uplink resource partitions. For example, a firstgroup of UEs may be assigned to a first partition of uplink resourcesfor sending their grant-free uplink transmissions. Each UE of the firstgroup of UEs may be assigned a different MA signature. A second group ofUEs may be assigned to a second partition of uplink resources forsending their grant-free uplink transmissions. Each UE of the secondgroup of UEs may be assigned a different MA signature. The MA signaturesin the first group may overlap with the MA signatures in the secondgroup, such that to uniquely identify the UE, the base station 100 mustknow both the MA signature of the uplink transmission and the partitionof uplink resources used to send the grant-free uplink transmission. Forexample, the base station 100 may use the detected MA signature 152 andan index corresponding to the grant-free uplink resource partition usedto check a lookup table to determine the identity of the UE that sentthe grant-free uplink transmission.

In embodiments in which the base station 100 can determine the identityof the UE without the UE ID 156, then the UE ID 156 may not even need tobe transmitted as part of the message 150.

In summary, various possibilities exist in implementation to allow forthe base station 100 to uniquely identify the UE that sent thegrant-free uplink transmission. For example, if only one UE is able touse a particular grant-free uplink resource, then the use of thatgrant-free uplink resource uniquely identifies the UE. As anotherexample, when there is a unique mapping of MA signatures to UEs for aparticular resource region, then the MA signature may uniquely identifya UE in that resource region. As another example, when a UE ID ispresent in the uplink message and successfully decoded by the basestation, the UE ID itself may uniquely identify the UE, or the UE ID incombination with another piece of information (e.g. the grant-freeuplink resource used) may uniquely identify the UE.

HARQ for Grant-Free Uplink Transmissions

HARQ may be performed for the grant-free uplink transmissions. Forexample, if the data 154 in the initial grant-free uplink transmissionis not successfully decoded by the base station 100, then aretransmission may be performed by the UE. The retransmission mayinclude a retransmission of the initial data and/or further informationfor decoding the initial data. For example, the retransmission data mayinclude some or all of the original data and/or parity information. Thebase station 100 may perform HARQ combining as follows: instead ofdiscarding unsuccessfully decoded initial data, the unsuccessfullydecoded initial data may be stored at the base station 100 in memory andcombined with received retransmission data to try to successfully decodethe initial data. When HARQ combining is performed, the retransmissiondata from the UE may not need to be a complete retransmission of theinitial data. The retransmission may carry less data, such as some orall of the parity bits associated with the initial data. One type ofHARQ combining that may be used is soft combining, such as chasecombining or incremental redundancy.

Initial transmissions and retransmissions may use different redundancyversions (RVs). When data is encoded in the grant-free message generator214, the encoded bits may be partitioned into different sets (thatpossibly overlap with each other). Each set is a different RV. Forexample, some RVs may have more parity bits than other RVs. Each RV isidentified by an RV index (e.g. RV 0, RV 1, RV 2, . . . etc.). When anuplink transmission is sent using a particular RV, then only the encodedbits corresponding to that RV are transmitted. Different channel codesmay be used to generate the encoded bits, e.g. turbo codes, low-densityparity-check (LDPC) codes, polar codes, etc. An error control coder (notillustrated) in the grant-free message generator 214 in the UE 102 a mayperform the channel coding.

In one embodiment, the channel coding results in an encoded bit streamcomprising three bit streams: a systematic bit stream and two parity bitstreams. Rate matching may be performed, and a circular buffer (notillustrated) may store the systematic and parity bits. The bits may beread from the circular buffer and modulated for transmission in thegrant-free uplink message. The circular buffer has different RVsassociated with it, e.g. four redundancy versions (RVs): RV0, RV1, RV2,and RV3. Each RV indicates a starting location from which the coded bitsare to be read from the circular buffer. Therefore, each RV transmits adifferent set of the encoded bits. Data may initially be transmittedusing RV 0, but a retransmission may sometimes use a higher RV, e.g., RV2 for the first retransmission, RV 3 for a second retransmission, etc.

The base station 100 uses knowledge of the RV to perform decoding. Forchase combining, the RV of the initial and retransmissions may be thesame, e.g. RV 0. For incremental redundancy, the retransmissions may usea higher RV that may follow a fixed pattern, e.g. RV 0 for the initialtransmission, RV 2 for the first retransmission, RV 3 for the secondretransmission, and RV 1 for the third retransmission. Therefore, inorder to decode the data, it may be necessary for the base station 100to know the RV index of the data being received in a grant-free uplinktransmission, unless there is only one predefined RV.

As part of the HARQ procedure for a grant-free uplink transmission, anACK may be sent by the base station 100 when the base station 100successfully decodes the data of the grant-free uplink transmission. Insome embodiments, a NACK may be sent by the base station 100 when thedata is not successfully decoded. However, a NACK may not always besent, e.g. in “NACK-less” HARQ schemes in which the absence of an ACKwithin a predetermined period of time is interpreted as a NACK. In someembodiments, an ACK may be associated with a UE ID that identifies theUE the ACK is meant for. If the MA signature and uplink grant-freeresource region used can together uniquely identify the UE, then the ACKmay instead be associated with an index identifying the MA signature.The UE knows the ACK is meant for it based on a matching MA signatureindex. A NACK, if sent, may be associated with a UE ID when the UE ID issuccessfully decoded by the base station. Alternatively, the NACK may beassociated with an index identifying the MA signature corresponding tothe uplink transmission being NACK'd, assuming successful activitydetection by the base station. Otherwise, the NACK may not be associatedwith a UE ID or a MA signature.

Retransmissions and Mapping to MA Signatures

If the data in the initial grant-free uplink transmission is notsuccessfully decoded by the base station, then a retransmission may beperformed by the UE. In some embodiments, the MA signature used in thegrant-free uplink transmission may identify whether the transmission isan initial transmission or a retransmission. In some embodiments, the MAsignature may also or instead be used to identify the UE that send thetransmission.

As a first example, FIG. 4 illustrates three tables 302, 304, and 306,showing different mappings. In table 302, the MA signature is areference signal. A pool {P} of nine reference signals (i.e. nine MAsignatures) are partitioned into three sets {P1}, {P2}, and {P3}. Thereference signals may be pilots. Each row in table 302 represents a3-tuple. In this example, the pool {P} is divided into three exclusivesets {P1}, {P2}, and {P3}, such that each set has three of the ninereference signals. Specifically, {P1} includes reference signals p11,p12, and p13, {P2} includes reference signals p21, p22, and p23, and{P3} includes reference signals p31, p32, and p33. Three of the ninereference signals are designated as initial reference signals, anotherthree of the nine reference signals are designated as firstretransmission reference signals, and the last three of the ninereference signals are designated as second retransmission referencesignals. The specific mapping in table 302 is only an example, and themapping may change over time and/or may only be for a particulargrant-free uplink resource partition (e.g. there may be a differentmapping in a different MA physical resource). In the example in table302, UE 102 a is assigned tuple index 1, UE 102 b is assigned tupleindex 2, and UE 102 c is assigned tuple index 3. Therefore, when thebase station 100 performs successful activity detection (i.e.successfully decodes the reference signal), then the base station 100uses the reference signal sequence to determine which UE sent thegrant-free uplink transmission. In the example in table 302, eachreference signal sequence also indicates to the base station 100 whetherthe grant-free uplink transmission is an initial transmission, a firstretransmission, or a second retransmission. In the example of table 302,the reference signal can be used to identify both the initial andretransmission as well as the UE identity. For example, reference signalp11, p21 or p31 may indicate the grant-free packets are transmitted byUE 102 a. In alternative embodiments, there may still be a uniquemapping between reference signals and UEs, but the reference signals mayonly be mapped to the identity of the UE and not mapped to initialtransmissions or retransmission. For example, reference signal p11 maybe assigned to a first UE, reference signal p12 may be assigned to asecond UE, . . . , and reference signal p33 may be assigned to a ninthUE. Each of the nine UEs may then use their same assigned referencesignal for their initial transmissions and retransmissions.

Table 304 is the same as table 302, except that the MA signature is asparse code multiple access (SCMA) codebook. Nine SCMA codebooks {A1,A2, A3, B1, B2, B3, C1, C2, and C3} are partitioned into initial andretransmission sets and assigned to each one of UEs 102 a-c. Forexample, the use of codebook A1 indicates to the base station 100 thatUE 102 a sent the transmission, and that the transmission is an initialdata transmission. In some embodiments, there may also be a fixed,semi-persistent, or dynamic association between certain referencesignals and SCMA codebooks. In such embodiments, the reference signalsequence or the SCMA codebook may be used to identify the UE and/orwhether the transmission is an initial transmission, a firstretransmission, or a second retransmission. In some embodiments, oneSCMA codebook may be associated with multiple reference signals. In suchembodiments, identifying the reference signal sequence reveals the SCMAcodebook used. In some embodiments, the SCMA codebook may have aone-to-one association with the reference signal. In such embodiments,identifying the reference signal sequence reveals the SCMA codebook usedand vice versa.

Table 306 is also the same as table 302, except instead of MAsignatures, there is an assigned mapping between physical uplinkresources used for the grant-free transmissions and initialtransmissions and retransmissions and UEs. Nine different time-frequencylocations {A1, A2, A3, B1, B2, B3, C1, C2, and C3} are partitioned intoinitial and retransmission sets and assigned to each one of UEs 102 a-c.For example, the receipt, by base station 100, of a grant-free uplinktransmission on physical uplink resources A1 indicates to the basestation 100 that UE 102 a sent the transmission, and that thetransmission is an initial data transmission.

In each table shown in FIG. 4, there happens to be a unique mappingbetween MA signatures tuples or physical resources tuples and the UEs.However, in some embodiments there does not have to be any uniquemapping to UEs. The base station does not have to assign UEs toparticular tuples. More generally, the mapping relationship between thedifferent MA signatures or physical resources, i.e. the tuples in thetables in FIG. 4, may be used to identify that the initial transmissionand the retransmissions belong to the same packet. For example, UE 102 amay randomly select index tuple 1 in table 302 (p11, p21, p31) for afirst data packet being transmitted to the base station 100, and UE 102a may randomly select index tuple 2 (p12, p22, p32) for a second datapacket being transmitted to the base station 100. In some embodiments, aUE may choose or be configured to use different tuples for differentpackets. In some embodiments, two UEs may choose the same tuple, e.g. ifthey randomly select MA signatures for the initial transmission, whichmay occur in mMTC applications.

In some embodiments, there may be a first MA signature used for aninitial transmission of a packet, and a second MA signature used for allK retransmissions of that packet, where K is greater than or equal toone. For example, table 308 in FIG. 5 illustrates an example in whichthe MA signatures are reference signals. A pool {P} of eight referencesignals are partitioned into two sets {P1} and {P2}. The referencesignals may be pilots. Each row in table 308 represents a 2-tuple. The2-tuples are not uniquely assigned to particular UEs, rather each UE ofa group of UEs may randomly select which 2-tuple to use. {P1} is a poolof initial transmission reference signals and includes reference signalsp11, p12, p13, and p14. {P2} is a pool of retransmission referencesignals and includes reference signals p21, p22, p23, and p24. When a UEis to transmit a packet using a grant-free uplink transmission, the UEuses one of the four 2-tuples. The 2-tuple used indicates whichreference signal is used for the initial transmission and whichreference signal is used for any and all K retransmissions. For example,if UE 102 a uses the 2-tuple indicated by index 2 for transmitting apacket, then the reference signal used for the initial transmission ofthe packet is p12, and the reference signal used for any and allretransmissions of the packet is p22.

In the embodiment described above in relation to FIG. 5, the MAsignature used identifies whether the grant-free uplink transmission isan initial transmission of data or a retransmission of the data.However, if K>1, then the retransmission MA signature does not revealwhether it is a first retransmission, second retransmission, etc. sincethe same MA signature is used for all retransmissions of the data.

Redundancy Version Identification

In some embodiments, there may be a mapping between MA signatures andRVs that may allow the base station 100 to determine the RV of thegrant-free uplink transmission, so that the RV does not have to beexplicitly signalled.

As an example, it may be preconfigured that each grant-free uplinktransmission can use only one of two RVs (e.g. RV 0 or RV 1). A first MAsignature is mapped to a first RV, such that when the base stationreceives the first MA signature, the base station knows that the data ofthe grant-free uplink transmission has the first RV. A second MAsignature is mapped to a second RV, such that when the base stationreceives the second MA signature, the base station knows that the dataof the grant-free uplink transmission has the second RV.

As a more specific example: each grant-free uplink transmission can useonly one of two RVs; when a UE is to transmit a packet using agrant-free uplink transmission, the UE uses one of the four 2-tuples ofFIG. 5; the reference signal in the 2-tuple that is used for the initialtransmission is mapped to the first RV, and the reference signal in the2-tuple that is used for the retransmission(s) is mapped to the secondRV. Then, when the base station 100 receives a grant-free uplinktransmission, the base station 100 knows from the MA signature usedwhether the grant-free uplink transmission is an initial transmission orretransmission of the data, and what the RV is for the data in thegrant-free uplink transmission.

In some embodiments, there may be first MA signature used for an initialtransmission of data and a second MA signature used for allretransmissions of that data, e.g. as in FIG. 5, but there may be morethan two possible RV values that may be used. In such embodiments, theMA signature may still be used to determine whether the grant-freeuplink transmission is an initial transmission or a retransmission. TheRV may then be identified based on this information, as well as based ona resource hopping pattern.

As an example, the receipt of a grant-free uplink transmission having afirst MA signature reveals to the base station 100 that the grant-freeuplink transmission is an initial transmission of data. The grant-freeuplink resource used to send the grant-free uplink transmission revealsto the base station 100 that the UE that sent the grant-free uplinktransmission is using a particular resource hopping pattern known inadvance to the UE and base station. The resource hopping patternspecifies the resources used for the initial transmission and anyretransmissions, and there is also a known mapping between the resourcehopping pattern and the RV used for the initial transmission and eachretransmission. Therefore, the base station can obtain from the mappingthe RV of the initial grant-free uplink transmission and the RV of allfuture grant-free uplink retransmissions of that data.

As another example, the receipt of a grant-free uplink transmissionhaving a second MA signature reveals to the base station 100 that thegrant-free uplink transmission is a retransmission of data. The basestation 100 has no record of a previous retransmission of the data, oreven an initial transmission of the data. The base station 100 decidesthat activity detection of the initial transmission must have failed andassumes that the received transmission is a first retransmission of thedata. The grant-free uplink resource used to send the firstretransmission reveals to the base station 100 that the UE is using aparticular resource hopping pattern known in advance to the UE and basestation. The resource hopping pattern specifies the resources used forthe initial transmission and any retransmissions, and there is also aknown mapping between the resource hopping pattern and the RV used forthe initial transmission and each retransmission. Therefore, the basestation can obtain from the mapping the RV of the first retransmissionand the RV of all future grant-free uplink retransmissions of that data.

As another example, the time slot used by the UE to send the grant-freeuplink transmission may correspond to a respective RV based on a mappingknown to both the UE and the base station. As a result, the duration oftime during which the grant-free uplink transmission is received by thebase station therefore reveals to the base station the RV used in thetransmission. For example, it may be configured in advance that whensending a grant-free uplink transmission in an odd time slot, the UEuses RV 0, and when sending a grant-free uplink transmission in an eventime slot, the UE uses RV 1.

FIG. 6 is a method performed by base station 100, according to oneembodiment. In step 402, the base station receives a grant-free uplinktransmission from UE 102 a. The grant-free uplink transmission utilizesan MA signature. In step 404, the base station 100 determines the RV ofdata in the grant-free uplink transmission using the MA signature. Instep 406, the base station 100 attempts to decode the data in thegrant-free uplink transmission based on the RV.

Step 404 may include using the MA signature to determine whether thegrant-free uplink transmission is an initial transmission of the data ora retransmission of the data, and then obtaining the RV based on boththe grant-free uplink resource used by the UE and the determination ofwhether the grant-free uplink transmission is an initial transmission ofthe data or a retransmission of the data.

Signaling ACK/NACK

There are many different possibilities for signaling an ACK or a NACK(when used) to a UE that has sent a grant-free uplink transmission.Different options are described below. A combination of two or more ofthe options described below may be used. Also, some of the optionsdescribed below assume that the base station has first uniquelyidentified the UE that sent the grant-free uplink transmission.Different ways in which the UE may be uniquely identified are describedearlier, e.g. using the UE ID (which may be an index), or using the UEID in combination with other information, such as the grant-free uplinkresource used, or using the MA signature in combination with thegrant-free uplink resource used, etc. Note that the ACK/NACK describedherein may not always be explicitly indicated, but may include anACK/NACK that is implicitly indicated by a scheduling grant. Forexample, sometimes the HARQ feedback is a scheduling grant that isscheduling a retransmission of the same transport block (TB) of thegrant-free transmission, which may implicitly indicate that the previousgrant-free transmission of the TB is not successful (i.e. a NACK). Inanother example, the base station may send HARQ feedback to the UE thatcontains a scheduling grant of a new TB using the same HARQ processnumber as the grant-free transmission, in which case, it may beconsidered that the grant includes an implicit ACK for the grant-freetransmission of the TB sharing the same HARQ process.

One Option—Dedicated Downlink Acknowledgement Channel

In some embodiments, the base station 100 may transmit ACKs and/or NACKsfor grant-free uplink transmissions on a dedicated downlinkacknowledgement channel. In some embodiments, the dedicated downlinkacknowledgement channel may be implemented in a similar way to thephysical HARQ indicator channel (PHICH) in LTE, in which case thededicated downlink acknowledgment channel may be called a “PHICH-like”channel.

In some embodiments, the feedback timing on the dedicated downlinkacknowledgement channel has a fixed relationship with the grant-freeresource access timing. For example, if a UE sends a grant-free uplinktransmission in subframe (or TTI) w, then the ACK/NACK for thatgrant-free uplink transmission is sent on the dedicated downlinkacknowledgement channel in subframe (or TTI) w+k. Ideally k is small,e.g. k=2. For example, if the UE is to automatically sendretransmissions until an ACK is received, then having k be a small valuewill hopefully result in earlier termination of the automaticretransmissions. In some embodiments, the value of k is predefined andknown to the UE and the base station. For example, the value of k may beconfigured in the system information. In some other embodiments, thevalue of k may be configured for each UE or UE group, and theconfiguration may be done through signalling, e.g. RRC signalling.

In some embodiments, the ACK/NACK feedback for a particular UE is senton the dedicated downlink acknowledgement channel using a particularorthogonal sequence. As an example, the ACK/NACK feedback for a UE maybe one bit that is repeated (to add redundancy) and then modulated usingbinary phase shift keying (BPSK) to result in a group of symbols. Thegroup of symbols are then multiplied using a particular orthogonalsequence. The output of those belonging to the same resource groups ortime-frequency locations are multiplexed together. A cell-specificscrambling may then be applied, followed by mapping to multiple resourceelements. The UE requires knowledge of which orthogonal sequence wasused in order to properly decode the ACK/NACK feedback. For example, theUE may perform a correlation of the orthogonal sequence with thereceived feedback signal to decode the ACK/NACK feedback. The orthogonalsequence is sometimes called an orthogonal code.

In some embodiments, there is a known mapping between (i) the MAsignature and/or the grant-free resources used by a UE to send thegrant-free uplink transmission, and (ii) the orthogonal sequence used bythe base station to send the ACK/NACK feedback and/or the time-frequencylocation in the dedicated downlink acknowledgement channel at which theACK/NACK feedback is sent. The mapping may be predetermined in advanceand may be stored in the form of a look-up table in the memory of theUEs and base station.

In some embodiments, the combination of the particular MA signature usedby the UE and the particular uplink grant-free resource region used bythe UE is indexed by (m, n), where m identifies the particular MAsignature used by the UE, and n identifies the particular uplinkgrant-free resource region used by the UE. The value (m, n) is mapped toa particular orthogonal sequence used for the ACK/NACK feedback and aparticular time-frequency location of the ACK/NACK feedback in thededicated downlink acknowledgement channel. In some embodiments, theparticular time-frequency location of the ACK/NACK feedback in thededicated downlink acknowledgement channel is called the “PHICH-likeresource group”.

As one example, table 420 in FIG. 7 illustrates an example mappingbetween (i) the MA signature (m) and the grant-free access region (n)used by the UE, and (ii) the orthogonal sequence used for the ACK/NACKfeedback for that UE and the time-frequency location of that ACK/NACKfeedback. In this example, there are four possible MA signatures thatmay be used by a UE for sending grant-free uplink transmissions, whichare indexed using values m=1, . . . 4. There are also four possibletime-frequency regions that may be used by the UE for sending thegrant-free uplink transmission, which are indexed using values n=1, . .. 4. The combination of MA signature used by the UE (m) and grant-freeregion used by the UE (n) maps to a specific orthogonal code andtime-frequency location in the dedicated downlink acknowledgementchannel. For example, if UE 102 a uses the MA signature identified byindex value m=3 and UE 102 a send its grant-free uplink transmissionusing the region of grant-free resources identified by index value n=1,then the UE knows from table 420 that the orthogonal sequence used forits ACK/NACK feedback in the dedicated downlink acknowledgement channelis orthogonal sequence C, and the time-frequency location of itsACK/NACK feedback in the dedicated downlink acknowledgement channel istime-frequency location i.

The orthogonal sequence and the time-frequency location in the dedicateddownlink acknowledgement channel may also be identified by an index. Forexample, in table 420, each (m, n) maps to a particular (x, y) where xidentifies the orthogonal sequence and x is A, B, C, or D, and where yidentifies the time-frequency location and y is i, ii, iii, or iv. x maybe referred to as the orthogonal sequence index, and y may be referredto as the resource group index (or PHICH-like resource group index). Theindex (x, y) is used by the UE to derive the orthogonal sequence to useto decode the feedback and the time-frequency location of the feedback.

Therefore, in operation, the UE may perform the following operations toreceive and decode its ACK/NACK feedback for a particular grant-freeuplink transmission sent by the UE. The UE first determines whichsubframe or TTI the downlink acknowledgment channel carrying itsfeedback is located based on the subframe or TTI used by the UE to sendthe grant-free uplink transmission (i.e. the w+k mentioned earlier). TheUE then maps the combination of its MA signature used (m) and grant-freeregion used (n) to index (x, y), e.g. as in table 420 of FIG. 7. Index(x, y) informs the UE of which orthogonal sequence to use to decode thefeedback and the time-frequency location of the feedback in thededicated downlink acknowledgement channel.

Table 420 in FIG. 7 is just an example. In some embodiments, acombination of m and n are needed to uniquely determine the orthogonalsequence used for the ACK/NACK feedback and the time-frequency locationof the ACK/NACK feedback. In other embodiments, as in table 420 in FIG.7, the value m uniquely maps to the orthogonal sequence used for theACK/NACK feedback and the value n uniquely maps to the time-frequencylocation of the ACK/NACK feedback, or vice versa. In some embodiments,there may only be one possible grant-free region that may be used by theUEs in a particular TTI, subframe or frame, in which case n alwaysequals 1, and the MA signature index m may be uniquely mapped to acombination of orthogonal sequence and the time-frequency location inthe dedicated downlink acknowledgement channel.

In some embodiments, the MA signature index m is a reference signalindex. In other embodiments, the MA signature index m maps to acombination of reference signal index and MAcodebook/signature/spreading sequence used. In some embodiments, thegrant-free access region index n may be represented by the first or lastphysical resource block (PRB) index.

In some embodiments, the reference signal index may be mapped to theorthogonal sequence index, and the combination of grant-free regionindex and MA codebook/signature/spreading sequence index may be mappedto the resource group index or the time-frequency location of thededicated DL acknowledge channel.

In some embodiments, if the UE identity can be determined by theactivity detection (e.g. the MA signature uniquely identifies the UE onthe grant-free uplink resources), then a UE index m may be used in placeof the MA signature index m. The UE index m may be an identifieruniquely associated with a UE for the grant-free access region. Forexample, if only 25 UEs can access the particular grant-free uplinkresources, then each one of the 25 UEs may be assigned a respective UEindex between “1” and “25”. The UE index is known to both the UE and thebase station. The UE index may be predefined or semi-staticallyconfigured. The UE index may be assigned as part of the radio resourcecontrol (RRC) signaling. If the UEs can only access one grant-freeuplink region in the particular frame, subframe, or TTI, then each UEindex may be mapped to a unique index value (x, y). If the UEs canaccess multiple grant-free regions in the particular frame, subframe, orTTI, then the UE index along with the grant-free region index togethermay be mapped to a unique index value (x, y).

In some embodiments, the feedback sent on the dedicated downlinkacknowledgement channel for a grant-free uplink transmission may be twobits (e.g. using QPSK). One of the bits may be used to indicate whetheractivity detection was successful, and the other one of the bits may beused to indicate whether decoding of the data was successful. In someembodiments, the two bits may be sent on different resources in thedownlink acknowledgment channel and/or using different orthogonalsequences. For example, a grant-free uplink transmission having aparticular (m, n) may be mapped to two index values (x, y), where eachone of the two index values (x, y) corresponds to a respective resourcelocation/orthogonal sequence conveying one of the two feedback bits.

Possible benefits of embodiments that use the dedicated downlinkacknowledgement channel (e.g. a PHICH-like channel) are as follows. Onlyone bit of feedback is sent before coding (‘1’=ACK, ‘0’, NACK or viceversa), which means possible savings in overhead. Also, there is no needto completely identify the UE, e.g. there is no need to identify the UE(Radio Network Temporary Identifier) RNTI, to send an ACK/NACK. Instead,the base station just needs to perform successful activity detection toobtain the MA signature (index m). The base station would know theuplink resources used (index n) for the grant-free uplink transmissionbased on the time-frequency location on which the uplink transmissionwas received. Possible disadvantages of embodiments that use thededicated downlink acknowledgement channel (e.g. a PHICH-like channel)are as follows. It may be harder to add additional information on top ofthe 1-bit ACK/NACK feedback, the method may only work well forsynchronous feedback, and reliability may be reduced due to not using aCRC.

FIG. 8 is a method performed by base station 100 and UE 102 a, accordingto one embodiment. In step 422, the UE 102 a transmits a grant-freeuplink transmission to the base station 100 on grant-free uplinkresources. The grant-free uplink transmission utilizes an MA signature.In step 424, the base station 100 receives the grant-free uplinktransmission. In step 426, the base station performs activity detectionto obtain the MA signature, and then attempts to decode data in thegrant-free uplink transmission. In step 428, the base station 100transmits, in a downlink acknowledgement channel, feedback relating tothe grant-free uplink transmission comprising an ACK or a NACK. Anorthogonal sequence used to convey the feedback and/or a time-frequencylocation of the feedback is based on at least one of the MA signatureand the grant-free uplink resources. In step 430 the ACK or NACK isreceived by UE 102 a on the downlink acknowledgement channel.

Another Option—Individual ACK/NACK Feedback

In some embodiments, the base station 100 may transmit ACKs and/or NACKsfor grant-free uplink transmissions for each individual UE. In someembodiments, the ACK/NACK feedback for an individual UE may betransmitted through downlink control information (DCI). Multiple DCIswould be transmitted separately when ACK/NACK feedback is beingtransmitted to multiple UEs, i.e. each UE would have its own individualDCI.

For example, the ACK or NACK for a particular UE may be included in DCIfor that UE that has a CRC field which is masked with the UE ID. The UEID may be the RNTI for the UE (e.g. the cell RNTI (C_RNTI)), althoughthis is not a necessity. If the UE ID is the RNTI for the UE, then theRNTI may be signalled through the RRC channel. The DCI may betransmitted at a location within the search space defined by the UE ID(e.g. defined by the C_RNTI). When monitoring the potential DCI command,the UE may attempt to decode all the possible locations of DCIs withinits search space. If the CRC checks with the assigned UE ID, then thecontrol channel is declared as valid and the UE processes theinformation inside the DCI.

In some embodiments, the RNTI used for retransmission of a grant-freetransmission and the RNTI used for grant-based transmission orretransmission of a grant-based transmission are different. We may callthe RNTI used for grant-free transmission as grant-free RNTI (GF-RNTI)or grant-free C-RNTI (GF C-RNTI), and the RNTI used for grant-basedtransmission as grant-based C-RNTI (GB C-RNTI). For example, GB C-RNTIcan be used for at least masking the CRC of a PDCCH used for ascheduling grant for grant-based transmission. The GF C-RNTI may beconfigured in UE specific RRC signaling. The GB C-RNTI may be configuredin UE specific RRC signaling or other UE specific signaling.

The search space location in the control channel (DCI) may be definedfor UEs operating in grant-free mode. In some embodiments, the searchspace location may be indicated by the index of potential CCEs (controlchannel elements) in each subframe/TTI. The index may have a predefinedrelationship derived from the grant free UE ID (such as the C_RNTI) orthe grant free group ID (such as a group_RNTI) assigned to the UE. Thegrant-free UE ID used to define the search space for the PDCCH can bethe GF C-RNTI or the GB C-RNTI. This method is similar to the definitionof PDCCH search space in LTE.

Another way to determine the search space is to explicitly signal thesearch space locations of DCI. The format provided may be atime-frequency region, within which the grant free UE should search forall CCEs. This explicit signaling may be carried out in RRC signaling.This is similar to ePDCCH search space defined in LTE, e.g., defined inePDCCH_Config in RRC signaling. In one embodiment, if an ACK/NACK is tobe sent to UE 102 a, then the ACK/NACK is included in the DCI for UE 102a. The encoder 210 in the base station 100 masks at least a portion ofthe DCI with the UE ID of UE 102 a. The masking may involve modifying atleast some of the information in the DCI using the UE ID of UE 102 a. Asan example, the CRC of the DCI may be masked by scrambling the CRC withthe UE ID of UE 102 a. The location in the downlink control channel atwhich the UE 102 a is to search for its DCI may be known by UE 102 abased on the UE ID of 102 a and/or based on the grant-free uplinkresources used by UE 102 a to send the grant-free uplink transmission.The UE 102 a searches the appropriate area of the downlink controlchannel for its DCI. Assuming the UE 102 a does not know the exacttime-frequency partition carrying its control information, then thedecoder 218 of UE 102 a blindly decodes the control information in itssearch area and tries to unscramble the CRC using the ID of UE 102 a. Anincorrect CRC is interpreted by the UE 102 a as an indication that thatparticular control information in the downlink control channel is notmeant for UE 102 a. A correct CRC indicates to UE 102 a that its DCI hasbeen correctly decoded. The UE 102 a can then retrieve the ACK or NACKfrom the decoded DCI. The UE ID can be in the payload of the DCI. The UEID can be a RNTI or a higher layer ID, the higher layer ID does not needto be tied to a specific cell and known by the base station and the UE.

The DCI decoded by UE 102 a may have different formats and may includedifferent information. As one example, the DCI may include a grant for aretransmission, indicating to the UE 102 a that the base station did notsuccessfully decode the initial grant-free uplink transmission. In suchinstances, a NACK may not be explicitly included in the DCI since a NACKis implicit by virtue of the fact that the DCI includes a grant for aretransmission. The grant may switch the grant-free transmission to agrant-based retransmission.

In some embodiments, the DCI has a relatively simple format, e.g. doesnot include information for a grant. As an example, the DCI could be assimple a one bit: ‘0’ for ACK and ‘1’ for NACK, or vice versa. In someembodiments, the DCI may include the identity of the UE if an ACK isbeing sent to the UE, and/or the DCI may contain the UE ID or (if the UEID is not known to the base station) the MA signature indexcorresponding to the MA signature in the uplink transmission if a NACKis being sent to the UE. In some embodiments, a particular UE may haveseveral grant-free uplink transmissions, in which case there may bemultiple HARQ processes.

In some embodiments, the DCI or the individual feedback channel thatcarries the ACK/NACK may also or instead include the HARQ process ID (orHARQ process number) for the packet being ACK'd/NACK'd. The ACK/NACK maycontain a HARQ process number (or HARQ process ID, or any attributesthat identify the HARQ process number or transport block (TB) index,e.g., MA signature index or grant-free access region index orcombination of the two) explicitly or implicitly, which is used toidentify which TB the ACK/NACK is used for if there are multiple TBstransmitted. The HARQ process ID may be implicitly or explicitlysignalled to the base station in the grant-free uplink transmission. Anexample of implicit signaling is if the HARQ process ID is identifiableto the base station based on the MA signature used by the UE. The MAsignature can be a reference signal or a codebook/signature/sequence orused for a multiple access (MA) scheme or any other attributes describedearlier. For example, if a MA scheme uses two different codebooks totransmit two TBs (corresponding to two HARQ processes). The base stationidentifies the codebook through activity detection. Then the basestation may indicate the codebook index or the corresponding HARQprocess index in the ACK/NACK, which identifies the TB that the ACK/NACKis for. In some embodiments, the HARQ process ID may be able to beimplicitly identified through different grant-free access regions. Forexample, if a UE is configured to be able to access two grant-freeaccess regions in one time slot. The UE may transmit two TBs thatcorrespond to two different HARQ processes. In the ACK/NACK feedback,the grant access region index or HARQ process ID may be indicatedimplicitly or explicitly such that the UE can identify which TB theACK/NACK feedback is for. An example of explicit signaling is to have afield in the grant-free uplink message that indicates the HARQ processID. The HARQ ID may be protected more robustly such that the basestation can identify it even if it may not be able to successfullydecode the data.

In some embodiments, the individual DCI may be transmitted together withother information for the UE, e.g. additional data to be transmitted tothe UE and/or a grant to send a retransmission of a current transportblock (TB) or new transmission of a new TB.

In general, the DCI used for HARQ feedback (ACK/NACK or grant) withrespect to a grant-free transmission may be associated with the GFC-RNTI or GB C-RNTI. In some embodiments, the UE ID used for the DCIused for the grant of a retransmission of a grant-free initialtransmission is the GF C-RNTI. In some other embodiments, the UE ID usedfor the DCI used for the grant of a retransmission of a grant-freeinitial transmission is the GB C-RNTI. The GF C-RNTI is used at least tomask the CRC of the DCI used for the retransmission of the grant-freeinitial transmission. Whether the DCI is used for the retransmission maybe identified by a new data indicator (NDI) field in the DCI. NDI may bea 1 bit field, which can be either 0 or 1. If the UE detects a DCI grantwith a CRC masked by GB C-RNTI, the UE may consider the grant aretransmission grant if NDI is not toggled with respect to the lastgrant of the same HARQ process. On the other hand, if there is a DCIgrant with a CRC masked by GB C-RNTI, and the NDI is toggled withrespect to the last grant of the same HARQ process, the UE may considerthe grant a scheduling grant of a new TB. In grant-free transmission,there is no scheduling grant for the initial grant-free transmission.Whether the DCI grant is for retransmission is determined by the fixedvalue of NDI field in the grant. For example, if after grant-freeinitial transmission, the UE detects a DCI with CRC masked by GF C-RNTIand the NDI field in the DCI equals to 1, UE may consider the DCI aretransmission grant of the initial grant-free transmission. Which TBthe retransmission is for can be identified by the UE using the HARQprocess ID included in the DCI. Note that there may be a configured orpredefined mapping between grant-free resources and the HARQ process ID,so that the UE knows which TB the HARQ ID corresponds to. On the otherhand, if the UE detects a DCI with CRC masked by GF C-RNTI and the NDIfield in the DCI equals to 0, the UE may consider the DCI an ACK of thegrant-free transmission. Which TB of the grant-free transmission the ACKcorresponds to may be identified by the HARQ process ID or numberincluded in the DCI. Note that in some embodiments, there is no explicitbit of ACK/NACK in the DCI. The UE can consider the DCI an ACK of the TBassociated with the HARQ process ID in the DCI if the DCI is associatedwith the GF C-RNTI and NDI=0. In some embodiments, if UE detects a DCIwith CRC masked by GF C-RNTI, the UE may consider it as a retransmissiongrant of the corresponding HARQ process regardless of the value of NDI,i.e., NDI here is not used to determine whether the grant is aretransmission grant. In some embodiments, the DCI used for indicatingan ACK of a grant-free TB may mask the CRC with the GB C-RNTI. If the UEdetects a DCI associated with the GB C-RNTI and the previoustransmission of the TB with the same HARQ process (identified by theHARQ process ID in the DCI) is a grant-free transmission, the UE mayconsider the DCI an ACK of the grant-free TB associated with the HARQprocess ID regardless of the NDI value. In some other embodiments, theUE only considers the DCI associated with GB C-RNTI an ACK of thegrant-free transmission if NDI=0. If the DCI associated with GB C-RNTIis used to indicate an ACK, the UE may also consider it as including ascheduling grant of a new TB with the included HARQ process ID. If theUE has data to transmit, the UE may transmit a new TB using the resourceconfigured in the DCI associated with GB C-RNTI. In some embodiments, ifthe DCI associated with GF C-RNTI is used to indicate an ACK, the UE maynot consider it as a scheduling grant of a new TB and may not transmit anew TB based on the grant. In some other embodiments, if the DCIassociated with GF C-RNTI is used to indicate an ACK, the UE may alsoconsider it as including a scheduling grant of a new TB with theincluded HARQ process ID. If the UE has data to transmit, the UE maytransmit a new TB using the resource configured in the DCI associatedwith GF C-RNTI.

Sending individual DCI typically requires the base station to uniquelydetermine the identity of the UE. In some embodiments, the base stationmay obtain the UE ID through decoding the data in the grant-free uplinktransmission. In embodiments in which, for a given region of grant-freeuplink resources, the MA signature uniquely identifies the UE, thendetection of the MA signature by the base station allows the basestation to uniquely identify the UE. The base station can then obtainthe UE ID for the UE, e.g. using a mapping between the MA signature andthe UE ID.

In some embodiments, the DCI may be used for termination of a continuousrepetition/retransmission. In some embodiments, the DCI format may besimilar to a current DCI format, such as DCI format 0 in LTE for uplinkscheduling. The HARQ-ACK message may be implicitly implied. For example,the DCI format that conveys a HARQ-ACK for termination of a continuousrepetition/retransmission may be similar to the DCI format used for LTEsemi-persistent scheduling (SPS) release PDCCH validation. In someembodiments, the DCI may be a new format that is used for ACK/NACKwithout a full grant.

In some embodiments, the DCI may contain a scheduling grant for aretransmission that switches the grant-free transmission to agrant-based retransmission. In some embodiments, the DCI may contain ascheduling grant for a new transmission of the UE that switches the newpacket of the grant-free UE to a grant-based transmission. The explicitgrant may implicitly imply an NACK feedback.

In some embodiments, the DCI may contain a scheduling grant for atransmission of a new TB, in which case, it may implicitly imply an ACKof a previous TB.

In some embodiments, the feedback channel may be transmitted through acontrol channel or data channel (and may not be in the format of DCI).The time-frequency location of the feedback channel may have a fixedrelationship with the time slot or subframe number or with thegrant-free transmission resource or with the combination of grant-freetransmission resource and MA signature used. The content inside thefeedback channel may be the UE ID being acknowledged or any contentdescribed earlier for the individual DCI.

In some embodiments, the location of the ACK/NACK for a UE in theindividual DCI may have a fixed timing relationship with the grant-freeuplink resources used to send the grant-free uplink transmission beingACK'd/NACK'd. For example, if a UE sends a grant-free uplinktransmissions in subframe (or TTI) w, then the ACK/NACK for thatgrant-free uplink transmission is sent in the DCI of subframe (or TTI)w+k. However, in some embodiments, the ACK/NACK may not necessarily havea fixed timing relationship with the grant-free resources. Inembodiments in which the HARQ process ID or any similar indication isincluded in the individual DCI for a UE, then the UE may be able toidentify which transport block (or packet) is acknowledged by using theHARQ process ID instead of the timing of the DCI. In some embodiments,the ACK/NACK sent on the individual DCI may be used for termination of acontinuous repetition. In this case, supporting individual DCItransmitted at an arbitrary timing may be beneficial.

Finally, as mentioned earlier in some embodiments, the individualACK/NACK for a UE does not have to be sent in DCI. Instead, for example,an ACK/NACK for a UE may be sent in a data channel, e.g. a PDSCH. Thelocation of the ACK/NACK in the data channel may be sent in the DCI. TheDCI indicating the location of the ACK/NACK may still be scrambled bythe UE ID in some embodiments. The HARQ feedback may be a UE specificDCI with CRC masked by the GF C-RNTI. The DCI may contain a schedulinggrant that schedules a PDSCH transmission. The actual ACK/NACK or HARQfeedback content may be transmitted in that data channel (PDSCH).

In some embodiments, the individual ACK/NACK may be sent in a feedbackchannel at a time-frequency location that has a fixed mappingrelationship with the combination of or one of the grant-free regionindex and MA signature index. In this scenario, the UE knows where tosearch for the feedback. The content of the feedback can be similar tothe case of sending ACK/NACK in the DCI, but it may not be in a formatof DCI. It may contain a CRC, but the CRC may or may not be masked bythe UE ID.

In some embodiments, the individual ACK/NACK channel may contain atleast one or some of, but not limited to:

-   -   a. The MA signature index that is identified through activity        detection or a combination of the MA signature index and the        grant-free access region index.    -   b. A UE ID if the UE is identified.    -   c. A HARQ process number that identifies which TB the feedback        corresponds to. Sometimes an attributes that identifies the HARQ        process number (e.g. a MA signature index, a codebook index        which identifies the HARQ process number) is included instead.        Sometimes, the HARQ process number may not be explicitly        included but can be derived from other attributes. The timing        advanced (TA) signal or timing information used to adjust uplink        timing for uplink synchronization if TA is estimated in the        initial grant-free transmission (e.g. using a preamble or a RS        for TA estimation).    -   d. A temporary identity, e.g., a TC-RNTI similar to the one        assigned in a LTE RAR message, used for further communications        between the UE and the network.    -   e. A scheduling grant, indicating the resource, including        time-frequency resource, MCS, reference signal, MA signature,        etc. that the UE will use for the following transmissions or        retransmissions.    -   f. Resource hopping pattern and/or RV hopping pattern, and/or MA        signature hopping pattern for the following        transmissions/retransmissions.    -   g. An explicit or implicit signal to indicate whether it is ACK        or NACK and optionally a signal to indicate whether the activity        detection successfully detects the MA signature.        FIG. 9 illustrates a method performed by base station 100 and UE        102 a, according to another embodiment. In step 423, the UE 102        a transmits a grant-free uplink transmission to the base station        100 on grant-free uplink resources. The grant-free uplink        transmission utilizes an MA signature. In step 425, the base        station 100 receives the grant-free uplink transmission. In step        427, the base station performs activity detection to obtain the        MA signature, and then attempts to decode data in the grant-free        uplink transmission. If the data is decoded, then the base        station 100 can obtain the UE ID (e.g. RNTI) of the UE 102 a. In        step 429, the base station 100 transmits, in individual downlink        control information, feedback relating to the grant-free uplink        transmission comprising an ACK or a NACK. If an ACK is sent, the        base station 100 masks the feedback using the UE ID, e.g. by        scrambling the CRC of the feedback with the UE ID. If a NACK is        sent, the base station 100 only masks the feedback using the UE        ID if the UE ID is known by the base station, e.g. if the MA        signature uniquely identifies UE 102 a on the grant-free uplink        resources. In step 431, the ACK or NACK is received by UE 102 a,        e.g. if the CRC is scrambled with the ID of UE 102 a, then the        UE 102 a receives the ACK or NACK by unscrambling the CRC using        the ID of UE 102 a.

Another Option—ACK/NACK in the Data Channel

In some embodiments, ACKs/NACKs are transmitted by the base station in adownlink data channel, e.g. in a physical downlink shared channel(PDSCH). A UE that sent a grant-free uplink transmission searches forDCI that indicates where in the data channel the ACK/NACK can be found.The DCI may be individual DCI, as above, in which case the DCI may bemasked using the UE ID (e.g. GF C-RNTI). Alternatively, the base station100 may transmit ACKs/NACKs for multiple UEs in the same resourcepartition of the downlink data channel. Every UE that sent a grant-freeuplink transmission that is to be ACK/NACK'd searches for the same DCI,which indicates the location of the resource partition having theACKs/NACKs. The DCI may contain a scheduling grant that schedules adownlink transmission in a data channel (e.g. a PDSCH). The actualACK/NACK or HARQ feedback content may be transmitted in that datachannel (PDSCH). The same DCI means it can be a group-common DCI asdescribed later in the disclosure. The DCI may be masked using a commonID value, e.g. a common RNTI, such as “GF_Common_RNTI”. The common IDvalue is known to each UE sending a grant-free uplink transmission andis used to decode the DCI. The common ID value may be predefined orindicated using RRC signaling. The common ID can be the same group RNTI(e.g. “GF_group_RNTI”) as described later in the group ACK/NACK of thisdisclosure.

The search space for the DCI in the downlink control channel may bebased on the grant-free uplink resources used.

As one example, ten UEs are configured to be able to send any grant-freeuplink transmission they may have on a first set of grant-free uplinkresources. The ten UEs are informed of the GF_Common_RNTI for the firstset of grant-free uplink resources. The ten UEs know to search aparticular area of the downlink control channel based on the location ofthe first set of grant-free uplink resources. The ten UEs each use theGF_Common_RNTI to decode the DCI. The DCI indicates where in thedownlink data channel the ACKs/NACKs for the ten UEs are located.

When ACKs/NACKs for multiple UEs are located in a common resourcepartition in the downlink data channel, e.g. as in the example in theparagraph above, then each ACK/NACK is associated with informationidentifying the UE to which the ACK/NACK belongs. The information may bethe UE ID, or an index identifying the MA signature transmitted in thegrant-free uplink transmission. In some embodiments, there may also beadditional information associated with an ACK/NACK. For example, a NACKfor a particular UE may have a grant associated with it that schedules agrant for a retransmission. Or the NACK may indicate that to the UE thatany retransmission is to be performed using a grant-free uplinktransmission, possibly using a particular resource hopping patternand/or RV hopping pattern, and/or MA signature hopping pattern.

Another Option—Group ACK/NACK

In some embodiments, a single ACK/NACK payload may acknowledge more thanone UE. Such an ACK/NACK will be referred to as a “group ACK/NACK”.

The UEs are divided into the different groups by the base station. Thegrouping may be based on which UEs are most likely to access the samegrant-free time-frequency uplink resources. In some embodiments, theremay only be one group, e.g. when there are only a small number of UEsthat can send grant-free uplink transmissions. The groups may be updatedover time. Each group has a respective group ID, e.g. “GF_group_RNTI”,which distinguishes the group from other groups. In embodiments in whichthere is only one group, the group ID may be predefined, or may not benecessary. In some embodiments, the group ID “GF_group_RNTI” may not beexplicitly signalled to the UE. The GF_group_RNTI may be predefined as afunction of at least one of the subframe or time slot number and framenumber and known to both the UE and the base station. In someembodiments, each grant-free access region may have its own respectivegroup ID, which may be known in advance. Grant-free access region canrefer to time-frequency resources that the UE can access to performgrant-free transmission. Different grant-free resource regions can referto different time-frequency locations. Different frequency locations canrefer to different frequency partitions, different bands or sub-bands,different carriers or sub-carriers, different bandwidth parts (BWP),different resource blocks (RBs) or resource block groups (RBGs) or ingeneral any different frequency unit or different frequency regionsassigned to the UE. Each UE in each group is assigned a position index,e.g. “GF_ack_index”. The position index identifies the UE from other UEsin the group. For example, if there are four UEs in a group, then one UEmay be assigned position index ‘1’, another UE is assigned positionindex ‘2’, another UE is assigned position index ‘3’, and the remainingUE is assigned position index ‘4’. In some embodiments, the UE positionindex may be semi-statically configured, e.g. in RRC signaling.

In some embodiments, higher layer signalling (such as RRC signalling) isused to assign UEs to groups, signal the group ID for each group, andassign a position index to each UE in each group. In some embodiments,the RRC signaling may also indicate to each UE how many other UEs are inthe same group.

In some embodiments, the UE position index may be replaced by acombination of grant-free access region index (sometimes the index isonly for the index within a time slot or a subframe) and MA signatureindex, in which case the index of the UE may not need to be signalled tothe UE in advance since the UE will know its index based on the MAsignature it uses and the grant-free resources it uses to send thegrant-free uplink transmission. In some embodiments, the grant-freeaccess region index can be an index of different frequency partitions,different bands or sub-bands, different carriers or sub-carriers,different bandwidth parts (BWP), different resource blocks (RBs) orresource block groups (RBGs) or in general index of different frequencyunit or different frequency regions assigned to the UE.

Once the groups are configured, a group ACK/NACK is used for each groupto acknowledge and/or negative acknowledge grant-free uplinktransmissions for UEs in that group. In some embodiments, the groupACK/NACK may ACK all received packets that are successfully decoded inone TTI or one time slot or one subframe.

In some embodiments, the group ACK/NACK is sent in a downlink controlchannel that is common to multiple UEs or addressed to a group of UEs.In such embodiments, the group ACK/NACK may be said to be sent viagroup-common DCI.

In some embodiments, the group-common DCI is sent at one of the searchspaces defined by the group ID (“GF_group_RNTI”). The definition ofsearch space is similar to the individual DCI. In some embodiments, thesearch space of the group-common DCI may be among common search spacesof the downlink control channel. In some scenarios, the search space maybe fixed for a group-common DCI such that no blind detection isnecessary. When monitoring the potential DCI command, the UE may attemptto decode all the possible locations of DCIs within its search space. Ifthe CRC checks with the assigned or derived group RNTI (GF_group_RNTI),the control channel is declared as valid and the UE processes theinformation inside the group-common DCI to obtain the group ACK/NACK.

In some embodiments, the location of the group ACK/NACK is based on thelocation of the time-frequency resources used to send the grant-freeuplink transmissions. There may be multiple group ACK/NACKs for eachtime slot (time slot can mean a time slot, a subframe, a TTi or ageneral time unit) with each group defined for each grant-free resource.For example, each time slot may contains 5 grant-free access regions atdifferent frequency locations, then all UEs that access the samegrant-free access region may form a group. In this case, the group ID(GF_group_RNTI) and UE position index may not need to be preconfiguredor signalled in advance. Each group may have a predefined group ID (e.g.GF_group_RNTI) that is a function of the grant-free access regionresources as well as the time slot index and frame number and known toboth the UE and base station. In other words, the group ID(GF_group_RNTI) may be derived as a function of the time unit as well asfrequency locations of the grant-free transmission resources used forthe grant-free transmission. In an example, there may be 5 grant-freegroups with 5 different GF_group_RNTIs corresponding to the 5 differentgrant-free access regions inside the time slot. In this case, the gNBmay send 5 separate group ACK/NACK through group DCI that is configuredby its corresponding group ID (GF_group_RNTI). The group DCI may be sentat a search space defined by the corresponding group RNTI and the CRCfor the group DCI may be masked by the same group ID (GF_group_RNTI). Ifa group of UEs send grant-free uplink transmissions at time-frequencylocation A, then search space B in the DCI is searched using the groupID associated with the grant-free access regions (resources) to obtainthe group ACK/NACK for those grant-free uplink transmissions. In someembodiments, search space B of the DCI may be a common search space forsending group-common DCI, which may or may not depend on the group ID.Each UE that sent a grant-free uplink transmission in the group of UEsblindly decodes the control information in search area B and tries tounscramble the CRC using the group ID associated with the grant-freeresources. An incorrect CRC is interpreted by the UE as an indicationthat that particular control information in the downlink control channelis not the group ACK/NACK. A correct CRC indicates to UE that its DCIhas been correctly decoded. The UE 102 a can then retrieve the groupACK/NACK from the decoded DCI. In some embodiments, blind detection maynot be needed, e.g. instead of search area B, the time-frequencyresources used to send the grant-free uplink transmissions map to aspecific known time-frequency location in the DCI to decode the groupACK/NACK. In some embodiments, the group ID is not used to scramble theCRC of the DCI.

As more specific example of the group ID (group RNTI) as a function ofthe time unit and/or frequency locations of the grant-free transmissionresources will now be explained. The group ID may be a function of atime resource index and frequency resource index, e.g.

GF_group_RNTI=f(t_index, f_index)

As a more specific example

GF_group_RNTI=A*t_index+B*f_index+C; where A, B, C are constants and *represents multiplication.

The frequency resource index/information f_index information may includeat least one of an index of different frequency partitions (e.g.frequency partition index), different bands or sub-bands (e.g. bandindex or sub-band index), different carriers or sub-carriers (e.g.carrier index or sub-carrier index), different bandwidth parts (BWP)(e.g. BWP index), different resource blocks (RBs) or resource blockgroups (RBGs) (e.g. RB index or RBG index) or in general index ofdifferent frequency units or different frequency regions (e.g. frequencyunit index or frequency region index).

The time resource index/information (t_index) may include at least oneof a system frame index, a sub-frame index, a slot index, a mini-slotindex, a symbol index. The grant-free resource information that is usedto calculate the group ID can be configured for the UE via broadcastsignaling, RRC signaling, DCI signaling or any combination of the abovethrough grant-free resource configuration. In the example above, thereare 5 grant-free groups with 5 different GF_group_RNTIs corresponding tothe 5 different grant-free access regions inside the time slot. The 5grant-free access regions can be 5 different frequency partitions, thefrequency partition can be 5 sub-bands with each containing a sub-bandindex or simply frequency partition index known to the UE by thegrant-free resource partition. Each UE and base station may derive thesame group RNTI as a function of the time index (e.g. the slot index)and the frequency location index (e.g. the subband or frequencypartition index). UEs that are accessing the same frequency partition(or the same grant-free access region) then share the same group RNTI orgroup ID. The derived group ID is then used to mask the CRC of the groupACK/NACK, which may be transmitted in group-common DCI. If the basestation sends a group-common DCI for each group, then there can be fivedifferent group-common DCI for the same slot. In some embodiments, thefrequency location index can be a RB index. However, if multiple RBs areused/defined for the grant-free transmission, the frequency index usedto calculate the group ID may be the starting or ending RB index.

In some embodiments, if a separate group ID and group ACK/NACK are usedfor different grant-free access regions in a time slot, then the UEposition index used in the group ACK/NACK may have a predefined mappingrelationship with the MA signature index.

In some embodiments, all of the UEs accessing the grant-free resourceregions in one time slot are sent feedback using one group ACK/NACKfeedback. A group ID GF_group_RNTI is defined for the group ACK/NACKfeedback. The GF_group_RNTI may be defined similarly as RA-RNTI definedfor random access in LTE. In some embodiments, the group ID(GF_group_RNTI) and the UE position index associated with the group canbe signalled to UE in advance (e.g. in RRC like described earlier). Insome other embodiments, the group ID (GF_group_RNTI) may be predefinedand known by all the grant-free UEs and the base station 100. TheGF_group_RNTI may be a function of time slot number and frame number,but still known by both the grant free UEs and the base station 100. Inthis scenario, the group ACK/NACK may be sent in one group-common DCIconfigured by this GF_group_RNTI. The DCI may be sent in a search spacedefined by the GF_group_RNTI and with a CRC masked by the GF_group_RNTI.Since the group ACK/NACK may contain ACK/NACK feedback for UEs accessingmultiple grant-free access regions for the time slot, the UE positionindex, if not configured in advance, may have a predefined mapping withthe combination of the grant-free access region index and MA signatureindex. The grant-free access region index can be any frequency locationindex, such as band or sub-band index, RB or RBG index, BWP index,carrier or sub-carrier index, frequency partition index etc. asdescribed earlier

In some embodiments, the group ACK/NACK may be a message having k fields(e.g. k bits), where each field is associated with a particular UEposition index and provides an indication of whether or not thegrant-free uplink transmission from that UE is acknowledged. As oneexample, a group may have k UEs and the group ACK/NACK may be a wordhaving k bits. Each bit in the word maps to a respective one of the kUEs. An example is illustrated in FIG. 10 at 434. A bit value of ‘1’means that a grant-free uplink transmission from the corresponding UEwas successfully received and decoded, i.e., an ACK. A bit value of ‘0’means NACK. If there is no ACK or NACK from a particular UE, then thebit corresponding to that UE is set to ‘0’. Therefore, if a UE in thegroup sends a grant-free uplink transmission and its position index inthe word 434 is ‘0’, then that UE does not know whether activitydetection was successful.

In some embodiments, the UE position index is preconfigured for thedefined group (GF_group_RNTI) in higher layer signalling (e.g. RRCsignalling), as described earlier. In some embodiments, the UE positionindex has a predefined mapping with the combination of the grant-freeaccess region index and MA signature index and known by both the UEs andgNB.

FIG. 11 illustrates a variation of FIG. 10 in which two bits b1 and b2are associated with each UE position index in word 436. Bit b1 indicateswhether or not activity detection was successful for the UE (e.g.‘1’=‘yes’), and bit b2 indicates whether or not the data wassuccessfully decoded (e.g. ‘1’=‘data successfully decoded’). The UE canuse the additional information to decide what to do next. For example,if the word 436 indicates that activity detection was not evensuccessful for the UE, then the UE may re-send the same initialtransmission with the same RV, whereas if the word 436 indicates thatactivity detection was successful but the data was not successfullydecoded for the UE, then the UE may send a retransmission using anotherRV (e.g. a higher RV).

In FIGS. 10 and 11, the UE position index may be based on an MAsignature index instead, or a combination of an MA signature index andan index indicating which grant-free uplink resources were used to sendthe grant-free uplink transmission.

In some embodiments, a particular UE may have several grant-free uplinktransmissions, in which case there may be multiple HARQ processes, eachHARQ process may indicate a TB. The HARQ process ID may be implicitly orexplicitly signaled to the base station in the grant-free uplinktransmission. An example of implicit signaling is if the HARQ process IDis identifiable to the base station based on the MA signature used bythe UE. An example of explicit signaling is to have a field in thegrant-free uplink message that indicates the HARQ process ID.

The position index may additionally include the HARQ process ID. FIG. 12illustrates an example of a group ACK/NACK that is the same as that inFIG. 11, but each HARQ process ID of each UE has its own set of bits b1and b2. There are N different possible HARQ process IDs for a UE. The UEknows where to look in word 438 based on its position index and its HARQprocess ID.

In other embodiments, one UE may be assigned multiple position indices,e.g. if the UE is using multiple MA signatures and/or if the UE hasmultiple HARQ process IDs. The UE would know which position index isassociated with the particular MA signature and/or particular HARQprocess ID corresponding to the UE's grant-free uplink transmission.

In some embodiments, the group ACK/NACK includes the UE ID for each UEthat the group ACK/NACK is acknowledging. In some embodiments, thepresence of the UE ID in the group ACK indicates to the UE that itsgrant-free uplink transmission was successfully received and decoded bythe base station. The absence of the UE ID indicates to the UE that itsgrant-free uplink transmission was not successfully decoded by the basestation, i.e., an implicit NACK. In some embodiments, instead ofincluding the UE ID, the group ACK includes, for each grant-free uplinktransmission that is being acknowledged, an index corresponding to theMA signature and grant-free uplink resource that was used.

FIG. 13 illustrates a group ACK/NACK 440, according to anotherembodiment. The group ACK/NACK 440 includes a field 442 indicating thenumber of UEs being ACK'd or NACK'd in the group ACK/NACK 440. Anotherfield 444 indicates the length of each UE ID. Another field 446indicates whether the UEs identified in the group ACK/NACK 440 are beingACK'd or NACK'd (e.g. ‘1’=ACK and ‘0’=NACK). The UE ID of each UE beingACK'd or NACK'd is then present in field 448. The group ACK/NACK isencoded as one payload and a CRC 450 is added. If the group ACK/NACK 440is sent through group-common DCI, the CRC 450 may be scrambled by agroup ID that is known by both the UE and base station.

Fields 442, 444, and 446 are optional. None or only some of fields 442,444, and 446 are included depending upon the implementation. Forexample, field 444 may be omitted if the UE ID is always a fixed lengthknown in advance to the UEs and base station, e.g. a fixed length UE IDobtained through activity detection and data decoding. As anotherexample, field 446 may be omitted if the presence of a UE ID alwaysmeans that UE is being ACK'd. Also, in some embodiments, CRC 450 may notbe present. Also, in some embodiments, each UE ID of some or all of theUE IDs in field 448 may be replaced with: (i) an index identifying theMA signature used by the UE sending the grant-free uplink transmissionbeing ACK'd/NACK'd; or (ii) a combination of an index identifying the MAsignature used by the UE and another index identifying the grant-freeuplink resources used by the UE.

In some embodiments, two separate group ACK/NACKs having the format ofFIG. 13 may be transmitted: one group ACK/NACK acknowledgingtransmissions, and another group ACK/NACK negative acknowledgingtransmissions. In other embodiments, a single group ACK/NACK may includeboth ACKs and NACKs. For example, fields 446 and 448 may be presenttwice: once acknowledging transmissions, and again to negativeacknowledge transmissions. In any case, if NACKs are being sent, thebase station may not have been able to identify the UEs being NACK'd, inwhich case a UE ID may be replaced with an MA signature index of theuplink transmission being NACK'd, or a combination of MA signature indexand an index identifying the grant-free uplink resource used by theuplink transmission being NACK'd. When there is both an ACK and a NACKfield, then a UE that sent a grant-free uplink transmission and thatdoes not see an ACK or a NACK in the group ACK/NACK knows that activitydetection of its grant-free uplink transmission was not evensuccessfully performed by the base station.

A group ACK/NACK that includes the UE ID for each UE being ACK'd/NACK'd(e.g. as in FIG. 13) may be shorter than a group ACK/NACK comprising abitmap (e.g. as in FIGS. 10 to 12) if there are a large number of UEsthat could potentially be ACK'd/NACK'd, but only a small subset of thelarge number of UEs is actually being ACK'd/NACK'd in the groupACK/NACK.

For all the formats described above (e.g. FIGS. 10 to 13), the groupACK/NACK may be transmitted in a downlink data channel (e.g. a PDSCH),in downlink control information (DCI), or in a feedback channel at aknown location that may not have the format of DCI.

In the embodiments in which the group ACK/NACK is transmitted in thegroup-common DCI, a group ID is pre-defined or signalled and the DCI istransmitted in the search space defined by the group ID (GF_group_RNTI).GF_group_RNTI can be configured in advance or predefined for a time slotor a grant-free region as described earlier. The CRC field in the DCI isalso usually masked with the group ID. More details of transmitting inthe DCI format are described earlier.

In the embodiments in which the group ACK/NACK is transmitted in adownlink shared channel (e.g. a PDSCH) instead of in downlink controlinformation (DCI), then the group ACK/NACK may still have any of theformats discussed above, e.g. in relation to FIGS. 10 to 13. In someembodiments, a downlink control channel (e.g. PDCCH) may indicate thelocation of the group ACK/NACK in the downlink shared channel. Thisindication may have the same format as a scheduling grant, but informingthe UEs in the group where to look for the group ACK/NACK in thedownlink data channel, what modulation was used for the group ACK/NACK,etc. In some embodiments, the indication may be in a DCI format and sentin a search space defined by the group ID (GF_group_RNTI) and with a CRCmasked or scrambled using the group ID. In some embodiments, theindication may be at a fixed location in the downlink control channelthat is known to the UEs in the group, in which case the UEs in thegroup do not have to search a search area in the downlink controlchannel using the group ID.

In some embodiments, the group ACK/NACK in the downlink data channel mayinclude other information for the UEs in the group, e.g. downlink datato be transmitted to one or more of the UEs in the group.

In some embodiments, the group ACK/NACK may be transmitted in a fixedtime-frequency location with respect to the time slot (subframe) or thegrant-free transmission resources or a combination of the two. The groupACK/NACK may still have any of the formats discussed above, e.g. inrelation to FIGS. 10 to 13. The feedback channel carrying the feedbackinformation may not necessarily be in DCI. It may not be necessary tohave a search space defined by a group ID, and a CRC may or may not needto be masked by the group ID.

In some embodiments, the group ACK/NACK transmitted through thegroup-common DCI may have a fixed timing relationship with the timing ofthe grant-free uplink resources used to send the grant-free uplinktransmissions being ACK'd/NACK'd, similar to the case of the PHICH-likechannel. For example, if a group of UEs send grant-free uplinktransmissions in subframe (or TTI) w, then the group ACK/NACK for thatgrant-free uplink transmission is sent in the DCI of subframe (or TTI)w+k. However, in some embodiments, the group ACK/NACK may notnecessarily have a fixed timing relationship with the grant-freeresources. In embodiments in which the HARQ process ID or any similarindication is included in the DCI, then the UE may be able to identifywhich transport block (or packet) is acknowledged by using the HARQprocess ID instead of the timing of the DCI. In some embodiments, thegroup ACK/NACK using group-common DCI may be used for termination of acontinuous repetition. In this case, supporting DCI transmitted at anarbitrary timing may be beneficial.

In some embodiments, the group ACK/NACK may contain a HARQ processnumber (or HARQ process ID, or any attributes that identifies the HARQprocess number or transport block (TB) index, e.g., MA signature indexor grant-free access region index or combination of the two) explicitlyor implicitly, which is used to identify which TB the group ACK/NACK isused for if there are multiple TBs transmitted. Some of the formats thatinclude the HARQ ID have been described earlier. The HARQ process ID maybe implicitly or explicitly signalled to the base station in thegrant-free uplink transmission. An example of implicit signaling is ifthe HARQ process ID is identifiable to the base station based on the MAsignature used by the UE. The MA signature can be a reference signal ora codebook/signature/sequence or used for a multiple access (MA) schemeor any other attributes described earlier. For example, if a MA schemeuses two different codebooks to transmit two TBs (corresponding to twoHARQ processes). The base station identifies the codebook throughactivity detection. Then the base station may indicate the codebookindex or the corresponding HARQ process index in the group ACK/NACK,which identifies the TB that the group ACK/NACK is for. In someembodiments, the HARQ process ID may be able to be implicitly identifiedthrough different grant-free access regions. For example, if a UE isconfigured to be able to access two grant-free access regions in onetime slot. The UE may transmit two TBs that correspond to two differentHARQ processes. In the group ACK/NACK feedback, the grant access regionindex or HARQ process ID may be indicated implicitly or explicitly suchthat the UE can identify which TB the group ACK/NACK feedback is for. Anexample of explicit signaling is to have a field in the grant-freeuplink message that indicates the HARQ process ID. The HARQ ID may beprotected more robustly such that the base station can identify it evenif it may not be able to successfully decode the data.

In some scenarios, the group ACK/NACK may only contain an ACK/NACK forone UE. In this case, all the group ACK/NACK signalling methods andformats described in this disclosure may be applicable for individualACK/NACK when the number of UEs in the group is one or the ACK/NACK istargeting one UE. As an example, if the number of UEs in the group isone, the HARQ feedback may be sent in a UE specific DCI as opposed to agroup-common DCI. The group RNTI can become the GF C-RNTI, and is usedto mask the DCI for the HARQ feedback and can be configured inUE-specific RRC signaling or derived based on the grant-freetransmission resources, e.g. at least the time and frequency resource ofthe grant-free transmission. The UE specific DCI may contain ACK/NACKbits corresponding to each HARQ process, but for only one UE. In thiscase, the UE specific DCI may contain a bit map, with each bitindicating an ACK or NACK for a respective HARQ process of the UE. Thelocation/position of each bit may have a predefined mapping with respectto a corresponding HARQ process (or HARQ process ID).

In some embodiments, the group ACK/NACK may comprise a single ACK/NACKpayload protected by a CRC. The payload may include an aggregation ofall UE IDs or MA signatures corresponding to uplink transmissions thatare being ACK/NACK'd. Each UE that sent a grant-free uplink transmissionthen decodes the group ACK/NACK to see if matching UE ID or MAsignatures can be found in the group ACK/NACK payload and whether itsgrant-free uplink transmission was acknowledged. In some embodiments, agroup ACK/NACK may be associated with a temporal group ID. The group IDmay be derived from the grant-free resources. For example, if a group ofUEs all use uplink resources C to respectively send a grant-free uplinktransmission, then that group of UEs may be associated with a group IDcorresponding to uplink resources C. In some embodiments, there may be aspecific 1-bit field indicating that the ACK/NACK is a group ACK/NACK,and the location of time and frequency resources of the ACK/NACK isdirectly linked to the grant free transmission resources and a group IDmay not be necessary. In some embodiments, there may be a reserved field(e.g. time-frequency location) in the downlink for sending a groupACK/NACK. The time-frequency location of the reserved field may bedetermined based on the location of the uplink resources used for thegrant-free uplink transmissions. For example, if a group of UEs eachsend their grant-free uplink transmission within time-frequency regionA, then the reserved field for the group ACK/NACK may be attime-frequency location B.

In all of the group ACK/NACK and individual ACK/NACK described in thisdisclosure (transmitted in a downlink control channel or downlink sharedchannel or any feedback channel in general), there may be additionalinformation transmitted in the feedback. The feedback content may besimilar to the random access response (RAR) message used for LTE randomaccess. In the group ACK/NACK, there may be multiple entries with eachentry corresponding to the feedback for a UE and either indexed by theMA signature index or explicitly includes the MA signature index. If thegroup ACK/NACK corresponds to the feedback of multiple grant-free accessregions, the entry may be indexed by a combination of the grant-freeaccess region index and MA signature index. Each entry may contains atleast one or some of, but not limited to:

a. The MA signature index that is identified through activity detectionor a combination of the MA signature index and the grant-free accessregion index.b. A UE ID if the UE is identified.c. A HARQ process number that identifies which TB the feedbackcorresponds to. Sometimes, an attribute that identifies the HARQ processnumber (e.g. a MA signature index, a codebook index which identifies theHARQ process number) is included instead. Sometimes, the HARQ processnumber may not be explicitly included but can be derived from otherattributes.d. The timing advanced (TA) signal or timing information used to adjustuplink timing for uplink synchronization if TA is estimated in theinitial grant-free transmission (e.g. using a preamble or a RS for TAestimation).e. A temporary identity, e.g., a TC-RNTI similar to the one assigned ina LTE RAR message, used for further communications between the UE andthe network.f. A scheduling grant, indicating the resource, including time-frequencyresource, MCS, reference signal, MA signature, etc. that the UE will usefor the following transmissions or retransmissions.g. Resource hopping pattern and/or RV hopping pattern, and/or MAsignature hopping pattern for the followingtransmissions/retransmissions.h. An explicit or implicit signal to indicate whether it is ACK or NACKand optionally a signal to indicate whether the activity detectionsuccessfully detects the MA signature.The above additional information may also be used for individualACK/NACK through individual DCI, individual control channel orindividual downlink shared channel (PDSCH).

FIG. 14 illustrates a method performed by base station 100 and UE 102 a,according to one embodiment. In step 452, the base station 100 assignsthe UE 102 a to a group, which has a corresponding GF_group_RNTI thatdistinguishes the group from other groups. In step 453, the base station100 determines the position index of UE 102 a in the group. In step 454,the base station 100 transmits to UE 102 a the GF_group_RNTI and theposition index assigned to UE 102 a, which is received by the UE 102 ain step 455. In step 456, the UE 102 a transmits a grant-free uplinkmessage utilizing an MA signature, which is received by the base station100 in step 457. In step 458, the base station performs activitydetection and attempts to decode the data. In step 459, the base station100 sends an ACK or a NACK for the UE 102 a in a group ACK/NACK. Thegroup ACK/NACK is sent on DCI. In step 460, the UE 102 a searches forthe group ACK/NACK in the search space defined by the GF_group_RNTI. Instep 461, the UE 102 a obtains the group ACK/NACK and reads its ACK orNACK at the position index of UE 102 a.

FIG. 15 is a method performed by base station 100 and UEs 102 a and 102b, according to one embodiment. In step 462, the UE 102 a transmits agrant-free uplink transmission to the base station 100, which isreceived by the base station 100 at step 464. In step 466, the UE 102 balso transmits a grant-free uplink transmission to the base station 100,which is received at step 468. Steps 462 and 464 may happen in parallelto steps 466 and 468. In step 470, the base station 100 transmits to UEs102 a and 102 b a group ACK/NACK, which may have any one of the formatsdiscussed above. The group ACK/NACK is received by both UE 102 a and 102b at step 472. In some embodiments, the group ACK/NACK may acknowledgeall UE packets received within a certain time window spanning a block oftime slots, TTIs, or subframes. Such a group ACK/NACK will be referredto as an “asynchronous” group ACK/NACK. The asynchronous group ACK/NACKmay be in a predefined location, or defined in a system informationblock (SIB), or configured using RRC.

Since an asynchronous group ACK/NACK may be acknowledging multiplepackets sent by the same UE (e.g. in different TTIs), each ACK in thegroup ACK/NACK is identified using both the UE ID (or MA signature if ituniquely identifies the UE) and other information that identifies thespecific packet being acknowledged. The other information may include,but is not limited to: the packet ID; and/or the packet arrival time;and/or an indication of the location of the packet, such as the subframeor resource block that the packet was sent on; and/or a HARQ process IDincluded in the packet. The asynchronous group ACK/NACK may be presentin a control channel, data channel, or dedicated acknowledgementchannel.

The asynchronous group ACK/NACK may have a similar format to thatdescribed for the group ACK/NACK in FIGS. 10 to 13. In the bit mapformat of FIGS. 10 to 12, the addition of packet ID, packet arrivaltime, subframe number, grant-free resource index, and/or HARQ ID can beadded to the UE position index. In the format of aggregated UE ID inFIG. 13, the packet ID, packet arrival time, subframe number, and/orgrant-free resource index can be added as a field alone or as a field ontop of each UE ID or as a group index. For example, the asynchronousgroup ACK/NACK may contain a number of groups, each group containing thegroup ACK/NACK for each time slot.

In some embodiments, an asynchronous group ACK/NACK may acknowledge allthe UE packets that arrived since the previous asynchronous groupACK/NACK was sent.

In some embodiments, the payload of the group ACK/NACK (asynchronous ornot) is encoded using a forward error correction (FEC) code and/or aCRC.

As mentioned above, a group ACK/NACK includes UE identify information(e.g. UE ID or MA signature) and/or packet identify information (e.g.packet ID or packet arrival time), for each uplink transmission beingacknowledged. In some embodiments, the UE identify information and/orthe packet identity information may be transmitted separately oraggregated and protected together. For example, as mentioned above, thegroup ACK/NACK may be a single payload protected by a CRC. The UEs knowwhere to look for the group ACK/NACK. For example, there may be adedicated channel for the group ACK/NACK, which is known to the UEs. Thegroup ACK/NACK location may be preconfigured, semi-persistentlyconfigured, or dynamically changed using a control channel.

FIG. 16 illustrates an example of an asynchronous group ACK/NACK. Atime-frequency partition is separated into five time slots. In the firsttime slot, UE 1 sends a first packet and UE 2 also sends a first packet,both via a respective grant-free uplink transmission. In a third slot,UE 1 transmits a second packet, UE 3 transmits a first packet, and UE 4transmits a first packet, each via a respective grant-free uplinktransmission. In a fourth time slot, UE 5 transmits a first packet in agrant-free uplink transmission. Then, after the end of the fifth timeslot, the base station sends an asynchronous group ACK/NACK for thepackets sent during the five time slots.

In some embodiments, the group ACK/NACK may also carry NACKs. Insituations in which the group ACK/NACK is only carrying NACKs (e.g. noUEs had their data successfully decoded), then the group ACK may beinterchangeably called a group NACK.

In some embodiments, the group ACK/NACK may be linked to the grant freeresources used. That is, if a group of UEs use a particulartime/frequency region or location A, then that group of UEs know whereto look for the group ACK/NACK, e.g. the group ACK/NACK is attime-frequency location B in a downlink acknowledgement channel.

In some embodiments, the group ACK/NACK may have a fixed associationwith the time of UE uplink transmission. For example, all UEs that senda grant-free uplink transmission at time A may have their transmissionsACK/NACK'd in the group ACK/NACK.

In some embodiments, the asynchronous group ACK/NACK may also betransmitted through a group-common DCI. In this case, there may be agroup ID (e.g. GF_group_RNTI) predefined. The group ID may change atdifferent predefined locations (e.g., as a function of frame number andsubframe or time slot number), but known to both the UEs sending thegrant-free uplink transmissions and the base station. The group-commonDCI may be sent at a search space defined by the group ID, and the CRCmay be masked using the group ID. In some embodiment, the asynchronousgroup ACK/NACK may be transmitted in a data channel indicated by a PDCCHthat is configured by the GF_group_RNTI.

Example Method of Signaling ACK/NACK

FIG. 17 is a method performed by the UE 102 a and the base station 100,according to one embodiment.

In step 502, the UE 102 a sends data to the base station in a grant-freeuplink transmission.

In step 504, the base station receives the grant-free uplinktransmission.

In step 506, the base station processes the grant-free uplinktransmission to determine the identity of UE 102 a. Step 506 maycomprise obtaining the UE ID for UE 102 a from the decoded data. Step506 may instead comprise obtaining the MA signature utilized by thegrant-free uplink transmission, after activity detection.

In step 508, the base station 100 transmits an ACK or NACK to UE 102 ausing one of the following methods: transmitting the ACK/NACK on adedicated downlink acknowledgement channel, or transmitting the ACK/NACKin individual DCI for the UE 102 a, or transmitting the ACK/NACK at aresource partition in a downlink data channel that is indicated via DCI,or transmitting the ACK/NACK as part of a group ACK/NACK. The details ofeach method are described above.

In step 510, the UE receives the ACK/NACK using a method correspondingto the method used by the base station 100 to send the ACK/NACK. Forexample, if the ACK/NACK was sent by the base station on a dedicateddownlink acknowledgement channel, then the UE 102 a obtains the ACK/NACKfrom the dedicated downlink acknowledgement channel.

Configuration of UE for Grant-Free Uplink Transmissions

A UE may be configured by the network (via the base station) forgrant-free uplink transmission. The configuration may changesemi-statically.

In one embodiment, the configuration is performed using RRC signalingand may include (but is not limited to) setting one, some, or all of thefollowing parameters:

(1) Whether the UE needs to monitor a downlink control channel. Ingrant-based uplink communications, a UE may regularly monitor a downlinkcontrol channel for DCI being communicated to the UE, e.g. to receive ascheduling grant for the UE. However, when the UE is configured toperform grant-free uplink transmissions, the UE may not need to monitorthe downlink control channel as frequently, or the UE may not need tomonitor the downlink control channel at all. How often (if at all) theUE performing grant-free uplink transmissions needs to monitor thedownlink control channel may be set by the network. For example, the UEperforming grant free uplink transmissions may be configured to monitorthe downlink control channel once every T subframes, where T is aparameter configured by the network.(2) The maximum number of retransmissions that may be performed by theUE. For example, the UE may be configured to keep sendingretransmissions until an ACK is received, but only up to a maximum of Kretransmissions. If K retransmissions have been sent and an ACK is stillnot received, then the UE no longer sends any retransmissions andconsiders the data not to have been received and correctly decoded bythe base station.(3) The resources that may be accessed by the UE for grant-free uplinktransmissions and retransmissions, e.g. the resource hopping patternused by the UE. In some embodiment, multiple resource hopping patternsor multiple grant-free time-frequency resources in a time slot areassigned to the same UE. In the case, when UE has multiple packets totransmit or needs multiple TBs to transmit data, the UE may choose totransmit the multiple TBs over different time-frequency resources. Forexample, if two grant-free time-frequency regions in one time slot areassigned to the same UE, the UE may use one grant-free region totransmit one packet associated with one TB and the other region totransmit another TB. Each TB may correspond to a different HARQ process.Each TB can be a transmission or retransmission of its corresponding TBindependently.(4) The MA signature tuples that are to be used, or that may be used, bythe UE for sending transmissions and retransmissions. For example, theUE may be assigned to a particular 3-tuple in table 302 of FIG. 4, or aparticular 2-tuple in table 308 of FIG. 5. The assignment may also orinstead include an MA signature hopping pattern, e.g. a patternindicating which reference signal is to be used for the initialtransmission, the first retransmission, the second retransmission, etc.(5) The MCS used by the UE for the grant-free uplink transmissions, andwhether (or by how much) the MCS is to be reduced after the initialtransmission. For example, an MCS hopping pattern may be assigned to theUE for the grant-free uplink transmission. An initial transmission mayhave a high MCS, a first retransmission may have a lower MCS, a secondretransmission may have an even lower MCS, etc.(6) Whether the UE needs to monitor for ACKs and/or NACKs after theinitial transmission, and whether a dedicated acknowledgement channelneeds to be monitored. The frequency of monitoring the acknowledgementchannel may also be configured. Also, or instead, the UE may be informedof which of the various options described earlier will be used forcommunicating the ACK/NACK, e.g. dedicated downlink acknowledgementchannel, individual DCI, downlink data channel, as part of a group ACK,and any relevant details.

Alternatively, some or all of the parameters above may be indicated viaDCI information instead of using the higher layer RRC signaling. The UEwould then be configured to check for the DCI. The DCI may include theresource configuration that enables the UE to perform the grant-freeuplink transmission, e.g. an assignment of which resources to use.

Another parameter not mentioned in (1) to (6) above, but that may beconfigured via the DCI, is:

(7) The resource in the subframe used for the grant-free uplinktransmission. As one example, the DCI may indicate the first resourceblock location in a subframe that the UE is permitted to send agrant-free uplink transmission. In some embodiments, knowledge of thefirst resource block location in the subframe may allow the UE todetermine the resource hopping pattern for future retransmissionsrelating to the packet, e.g. if there is a known mapping between aresource used for a grant-free uplink transmission and a correspondinghopping pattern having that resource.

Grant-Free Repetitions and Grant-Free to Grant-Based Switch

There may be situations in which it is beneficial for a UE to switchbetween grant-free uplink transmissions and grant-based uplinktransmissions.

Scheduling an uplink transmission for a UE in response to receiving agrant-free uplink transmission may be referred to as a “grant-free togrant-based switch”, i.e. a grant-free uplink transmission is receivedfrom a UE, and in response a grant-based uplink transmission isscheduled for that UE by the base station. A grant-free to grant-basedswitch may be performed by sending a scheduling grant to the UE thatsent the grant-free uplink transmission.

In some embodiments, the base station 100 may perform a grant-free togrant-based switch based on certain conditions. Any one condition, orany combination of conditions, may be used by the base station 100 todetermine whether to perform a grant-free to grant-based switch. Exampleconditions include:

(A) The grant-free message includes a buffer status report indicatingthat the UE has data (or more data) to send. In response, the basestation 100 may perform a grant-free to grant-based switch.and/or(B) The data in the grant-free message is unsuccessfully decoded. Inresponse, the base station 100 may perform a grant-free to grant-basedswitch.and/or(C) Latency requirement. If a UE is close to its latency bound, then thebase station 100 may perform a grant-free to grant-based switch.Otherwise, the base station 100 may not perform the switch, in whichcase the base station 100 may just send an ACK or NACK without ascheduling grant, or the base station 100 may not send anything. Anysubsequent transmissions (or retransmissions) by the UE may then be sentvia grant-free uplink transmissions. More generally, regardless oflatency requirement, if the base station 100 determines that agrant-free to grant-based switch for a UE is not to be performed, thenthat UE may continue grant-free transmissions/retransmissions.and/or(D) Number of transmissions. For example, if a UE has sent several (e.g.three) retransmissions of data via grant-free uplink transmission, anddecoding of the data by the base station still fails, then the basestation may perform a grant-free to grant-based switch by sending ascheduling grant for the next retransmission. In some embodiments, thenumber of retransmissions may be determined by a reference signalidentification (e.g. the reference signal used in the retransmission) orby a separate indicator sent by the UE in the grant-free uplinktransmission.and/or(E) The UE may send an indicator that indicates whether the UE desiresto switch to grant-based uplink transmission, based on the UE's knowncircumstances or requirements (e.g., the UE's latency requirement,traffic load, channel conditions, etc.). The base station 100 mayperform a grant-free to grant-based switch if the UE indicates a desireto switch to grant-based uplink transmission.and/or(F) The traffic load of grant-free UEs, e.g. the number of grant-freeUEs that arrive in a current or recent subframe(s). If the number ofgrant-free uplink transmissions and/or the number of UEs permitted tosend grant-free uplink transmissions exceeds a certain threshold, thenin response a grant-free to grant-based switch may be performed for oneor more UEs.and/or(G) If there is a potential future collision from a currently detectedUE operating in grant-free transmission mode, then a grant-free togrant-based switch may be performed to try to avoid the potential futurecollision.and/or(H) Quality of Service (QoS) requirements. Depending upon the QoSrequirements of a UE sending a grant-free uplink transmission, agrant-free to grant-based switch may be performed for that UE.

In some embodiments, the DCI and/or scheduling information for thegrant-free to grant-based switch may also include some or all of thefollowing information:

(i) An indicator indicating whether, after the granted uplinktransmission, the UE is to send further uplinktransmissions/retransmissions via grant-free uplink transmissions, orwhether the UE is to continue in grant-based mode, i.e. wait for futuregrants before sending further uplink transmissions/retransmissions. Inone embodiment, the indicator may be a value that is “true” by default.A value of “true” indicates to the UE that any retransmissions sentafter the granted uplink transmission are to be sent via grant-freeuplink transmissions and are to continue without waiting for anACK/NACK, until an ACK is received (or until the maximum number K ofretransmissions has been reached). A value of “false” indicates to theUE that any retransmissions sent after the granted uplink transmissionare to be sent via grant-based uplink transmissions.and/or(ii) An indicator indicating whether the grant is for a single granteduplink transmission, or whether the UE is granted to perform multipletransmissions, e.g. multiple retransmissions. If the UE is granted toperform multiple transmissions, then the indicator may indicate one,some, or all of the following: (a) the maximum number of retransmissionsK (e.g. item (2) above); and/or(b) the resource block assignment for the first transmission (e.g. item(7) above) and/or the resource hopping pattern; and/or (c) the MAsignature for the first transmission and/or the MA signature hoppingpattern (e.g. item (4) above); and/or (d) the MCS for the initialtransmission or an MCS hopping pattern (e.g. item (5) above).

Items (i) and/or (ii) may also be included in the DCI and/or schedulinginformation for a granted uplink communication that is not a grant-freeto grant-based switch. For example, a UE may be operating in grant-basedmode, but the indicators in (i) and (ii) above may also be included inthe DCI and/or scheduling information for some or all of the granteduplink communications to configure a UE for follow-up behaviour.

In some embodiments, UE 102 a may be configured to send an initialtransmission of a transport block (TB) (e.g. of a packet), and thenautomatically perform retransmissions of the TB via subsequentgrant-free uplink transmissions. The automatic grant-freeretransmissions may be referred to as performing continuous repetitionsof the TB. That is, an initial uplink transmission of the TB may beperformed, followed by continuous repetition of the TB using subsequentgrant-free uplink transmissions. The initial transmission may begrant-free or granted.

In some embodiments, the repetitions of the TB may use differentredundancy versions, e.g. RV 1 for the first repetition, RV 2 for thesecond repetition, etc. However, the redundancy versions do not have tobe different. In some embodiments, repetitions of the TB may usedifferent MCS, e.g. the initial transmission may have a high MCS, thefirst repetition may have a lower MCS, the second repetition may have aneven lower MCS, etc. However, the MCS of different repetitions do nothave to be different.

In some embodiments, the repetition may be performed on preconfiguredresources or preconfigured hopping patterns. For example, based on thegrant-free resources used by UE 102 a to send the initial transmission,there may be fixed future resources predetermined in advance for sendingany repetitions related to the initial transmission. For example, if theinitial grant-free transmission uses time-frequency location A in afirst TTI, then the first repetition is to be sent at time-frequencylocation B in the next TTI, and the second repetition is to be sent attime-frequency location C in the following TTI, etc.

The continuous repetitions may be performed by UE 102 a until at leastone of the following conditions is met:

(1) A message is received from the base station 100 indicating that thebase station 100 has successfully received and decoded the TB. Themessage may be an ACK, or at least will be called an “ACK” herein sincethe message acknowledges the TB has been successfully decoded. The ACKmay have any one of the formats described earlier (e.g. sent in adedicated downlink acknowledgement cannel, sent as individual DCI, sentin a data channel, sent as part of a group ACK/NACK having any of theformats of FIGS. 10-13, etc.). In some embodiments, the ACK may includea grant for UE 102 a to send one or more additional TBs. If a grant isincluded as part of the ACK, then the ACK does not actually have to beexplicitly included. That is, if UE 102 a sends a first TB in agrant-free uplink transmission, and in response receives a grant for theUE 102 a to send one or more additional TBs, then the UE 102 a assumesthat the first TB was successfully decoded by the base station 100. TheACK is implicit by virtue of the fact that the UE 102 a received thegrant to send more TBs. In some embodiments, theacknowledgment/indication of successful receipt of the TB is in an ULgrant from the base station. As described earlier, the ACK feedback maycontain a HARQ process number (or HARQ process ID, or any attributesthat identify the HARQ process number or TB index, e.g., MA signatureindex or grant-free access region index or combination of the two) whichis used to identify which TB the ACK is meant for if there are multipleTBs transmitted. The HARQ process ID may be implicitly or explicitlysignalled to the base station in the grant-free uplink transmission. Anexample of implicit signaling is if the HARQ process ID is identifiableto the base station based on the MA signature used by the UE. The MAsignature can be a reference signal or a codebook/signature/sequenceused for a multiple access (MA) scheme or any other attributes describedearlier. For example, if a MA scheme uses two different codebooks totransmit two TBs (corresponding to two HARQ processes). The base stationidentifies the codebook through activity detection. Then the basestation may indicate the codebook index or the corresponding HARQprocess index in the grant, which identifies the TB that the ACK is for.In some embodiments, the HARQ process ID may be able to be implicitlyidentified through different grant-free access regions. For example, ifa UE is configured to be able to access two grant-free access regions inone time slot. The UE may transmit two TBs that correspond to twodifferent HARQ process. In the UL grant, the grant access region indexor HARQ process ID may be indicated implicitly or explicitly such thatthe UE can identify which TB the ACK is for. An example of explicitsignaling is to have a field in the grant-free uplink message thatindicates the HARQ process ID. The HARQ ID may be protected morerobustly such that the base station can identify it even if it may notbe able to successfully decode the data.

and/or

(2) The number of repetitions for the TB reaches K. That is, if the UE102 a has performed K retransmissions and an ACK is still not receivedfrom the base station 100, then the UE 102 a gives up trying to send theTB to the base station 100. In some embodiments, K is semi-staticallyconfigured by the base station 100, such that the base station100/network can adjust K over time.

and/or

(3) A grant is received from the base station performing a grant-free togrant-based switch, i.e. the base station 100 sends a grant to UE 102 ato perform one or more of the retransmissions. If an uplink grant issuccessfully received for a slot/mini-slot for the TB, the uplink grantallocation overrides the grant-free allocation for that slot/mini-slotfor that TB, and the UE's transmission/retransmission follows the uplinkgrant for that slot/mini-slot for that TB. As described earlier, thegrant may contain a HARQ process number (or HARQ process ID, or anyattributes that identifies the HARQ process number or TB index, e.g., MAsignature index or grant-free access region index or combination of thetwo) which is used to identify which TB the grant is meant for if thereare multiple TBs transmitted. The HARQ process ID may be implicitly orexplicitly signalled to the base station in the grant-free uplinktransmission. An example of implicit signaling is if the HARQ process IDis identifiable to the base station based on the MA signature used bythe UE. The MA signature can be a RS or a codebook/signature/sequenceused for a multiple access (MA) scheme or any other attributes describedearlier. For example, if a MA scheme uses two different codebooks totransmit two TBs (corresponding to two HARQ processes). The base stationidentifies the codebook through activity detection. Then the basestation may indicate the codebook index or the corresponding HARQprocess index in the grant, which identifies the TB that the grant isfor. In some embodiments, the HARQ process ID may be able to beimplicitly identified through different grant-free access regions. Forexample, if a UE is configured to be able to access two grant-freeaccess regions in one time slot. The UE may transmit two TBs thatcorrespond to two different HARQ process. In the UL grant, the grantaccess region index or HARQ process ID may be indicated implicitly orexplicitly such that the UE can identify which TB the grant is for. Anexample of explicit signaling is to have a field in the grant-freeuplink message that indicates the HARQ process ID. The HARQ ID may beprotected more robustly such that the base station can identify it evenif it may not be able to successfully decode the data. Note that thisdoes not assume that the uplink grant is scheduled based on the slotwhere grant free allocation is based on mini-slot (vice versa).

As mentioned above, in some embodiments a grant-free to grant-basedswitch may occur to grant a retransmission after an initial transmissionis sent via a grant-free uplink transmission. For example, the UE 102 amay send an initial transmission, and in response the base station 100may perform successful activity detection but not successfully decodethe data in the initial transmission. The base station 100 thereforesends a grant to UE 102 a to send one or more retransmissions.

In some embodiments, if the uplink grant for the retransmission isreceived at time slot n, and the grant indicates a grant ofretransmission at time slot n+k (where k≥0), then UE 102 a has twooptions:

(1) In case in which k>1, the UE 102 a performs continuous grant-freerepetition from slot n+1 to slot n+k−1, and then switches to thegrant-based retransmission on slot n+k. If k=1 then the UE 102 a wouldperform the grant-based retransmission in the next slot, n+1.or(2) In case in which k>1, the UE 102 a stops performing grant-freerepetitions after slot n (i.e., does not perform grant-free repetitionat time slot n+1 or any subsequent time slots), and UE 102 a waits untilslot n+k to perform the grant-based retransmission according to thegrant. If k=1 then the UE 102 a would perform the grant-basedretransmission in the next slot, n+1.

FIG. 18 is a method performed by base station 100 and UE 102 a,according to one embodiment. In step 552, UE 102 a sends an initialgrant-free transmission of a TB on a grant-free uplink resource, andutilizing an MA signature. In step 554, the base station 100 receivesthe uplink transmission. In step 556, the base station 100 successfullyperforms activity detection to identify the MA signature, but the basestation 100 is unable to successfully decode the data in the TB. In step558, the base station 100 therefore sends a grant to the UE 102 a. Thegrant schedules a retransmission of the TB in later time slot n+k. Instep 560, the grant is received by UE 102 a at time slot n. In step 562,the UE 102 a sends the granted retransmission, which is received by thebase station 100 in step 564. In one embodiment, between steps 560 and562 the UE 102 a performs continuous grant-free repetition for the TB,e.g. from slot n+1 to slot n+k−1. In another embodiment, after step 560the UE 102 a does not send any grant-free repetitions of the TB, butinstead waits and only sends the granted retransmission in step 562.

FIG. 19 is a method performed by UE 102 a, according to one embodiment.

In step 602, the UE 102 a receives from base station 100 a messageconfiguring parameters for one or more grant-free uplink communications.

In step 604, the UE 102 a decodes the message to obtain the parameters.The parameters include: whether and/or how often the UE is to monitor adownlink control channel; and/or a maximum number of retransmissionsthat may be performed by the UE; and/or resources that may be accessedby the UE for grant-free uplink transmissions and retransmissions;and/or at least one MA signature that is to be used by the UE; and/orthe MCS used by the UE; and/or whether the UE needs to monitor for ACKsand/or NACKs after the initial transmission, and/or whether a dedicatedacknowledgement channel needs to be monitored; and/or a resource in asubframe used for a grant-free uplink transmission.

HARQ Feedback

Many different HARQ feedback scenarios are provided above for grant-freeuplink transmissions. The following applies to all of the scenariosabove, whether there is continued repetition or not, or whether thegrant-free uplink transmission is an initial transmission or aretransmission.

A TB is sent from the UE 102 a to the base station 100 using agrant-free uplink transmission. In response, HARQ feedback (e.g. anACK/NACK, a grant, etc.) for the grant-free uplink transmission isprovided by the base station 100 to the UE 102 a. In some embodiments,an acknowledgment/indication of successful receipt of the TB (e.g. anACK) is in the form of an uplink grant from the base station 100. Asdescribed earlier, in some embodiments the ACK/NACK feedback may containa HARQ process number (or HARQ process ID, or any attributes thatidentify the HARQ process number or TB index, e.g., MA signature indexor grant-free access region index or combination of the two), which isused to identify which TB the ACK/NACK is meant for if there aremultiple TBs transmitted. The HARQ process ID may be implicitly orexplicitly signalled to the base station 100 in the grant-free uplinktransmission from UE 102 a. An example of implicit signaling is if theHARQ process ID is identifiable to the base station 100 based on the MAsignature used by the UE 102 a in the grant-free uplink transmission.The MA signature may be a reference signal or acodebook/signature/sequence used for a multiple access (MA) scheme, orany other attributes described earlier. For example, if a MA scheme usestwo different codebooks to transmit two TBs (corresponding to two HARQprocesses). The base station 100 identifies the codebook throughactivity detection. Then, the base station 100 may indicate the codebookindex or the corresponding HARQ process index in its grant, whichidentifies the TB that the ACK is for. In some embodiments, the HARQprocess ID may be able to be implicitly identified by the base station100 through different grant-free access regions. For example, if a UE102 a is configured to be able to access two grant-free access regionsin one time slot. The UE 102 a may transmit two TBs that correspond totwo different HARQ processes. In the uplink grant from the base station100, the grant access region index or HARQ process ID may be indicatedimplicitly or explicitly, such that the UE 102 a can identify which TBthe ACK is for. An example of explicit signaling is to have a field inthe grant-free uplink message that indicates the HARQ process ID. TheHARQ ID may be protected more robustly such that the base station 100can identify it even if it may not be able to successfully decode thedata.

For all the HARQ feedback (ACK/NACK and/or grant) signaling, a UE'scontinuous grant-free repetitions may be optionally stopped early by agrant or optionally stopped early by an ACK before finishing the Krepetitions. For example, if the UE received an ACK during the Krepetitions, the UE may stop further repetitions if the number ofrepetitions has not reached K. In some other scenarios, the UE mayperform continuous repetition until either the repetition reaches K oran uplink grant is received. The ACK can be in any of the signalingformats described in this disclosure (e.g. it can be a group-common DCIor UE specific DCI). If a scheduling grant is received during or after Krepetitions, which schedules a retransmission of the same TB, then theUE will switch to grant-based retransmission of the TB in the resourceconfigured in the scheduling grant.

In some embodiments, if the UE finishes K repetitions of a TB, and theUE has not received HARQ feedback (e.g. an ACK/NACK or grant) yet, theUE may wait for HARQ feedback (ACK/NACK or grant). If the UE does notreceive an ACK or grant from the base station within a predefined windowT1 after the K repetitions are transmitted, then the UE may assume NACKand perform grant-free retransmissions of the TB. Grant-freeretransmissions may be done on configured grant-free resources.Grant-free retransmissions may include another set of K repetitions. Insome other embodiments, if the UE does not receive a NACK or grant fromthe base station within the predefined/configured window T1 after the Krepetitions, the UE may assume ACK and not to perform any furtherretransmissions until being further scheduled. In some otherembodiments, it is up to UE's implementation whether to perform furthergrant-free retransmissions if no HARQ feedback is received within thepredefined time window after the K repetitions. There may be anotherpredefined/configured time window T2 (starting from the time of initialgrant-free transmission) or maximum number of grant-free retransmissionsN a UE can perform such that if the time window is reached or themaximum number of grant-free retransmissions are performed by the UE,then the UE should not perform any more grant-freeretransmission/repetition without feedback from the base station. Theparameters T1, T2 or N can be predefined or configured in UE specificRRC signaling.

In some embodiments, the UE may flush the buffer of the TB immediatelyif an ACK is received for the TB during or after the K repetitions. TheACK can be in any of the signaling forms described in the disclosure. Insome other embodiments, the UE may simply hold off furtherrepetition/retransmission of the same TB when an ACK is received. The UEmay only flush the HARQ buffer of the TB of a grant-free transmission ifan uplink grant is received that schedules a new TB that is using thesame HARQ process (or HARQ process ID) of the TB. In some embodiments,if the UE does not receive a NACK or grant from the base station withinthe predefined/configured window T1 after finishing transmission of theK repetitions, the UE may assume ACK and flush the buffer of the TB, orthe UE may assume ACK and not flush the buffer and not perform anyfurther retransmission until being further scheduled.

If grant-free retransmission is to be performed by the UE after notreceiving any feedback within a window of K repetitions, the UE mayperform the grant-free retransmission on any of the grant-free resourcesregardless of the corresponding HARQ process ID. In some otherembodiments, the UE may only be permitted to perform grant-freeretransmission on a grant-free resource that is mapped to the same HARQprocess ID of the grant-free initial transmission. The describedprocedure also works for the case where K=1.

In one uplink grant-free transmission mode, the UE can performgrant-free transmission after RRC signaling without DCIsignaling/activation. The UE first performs an initial access process.The base station then selects the grant-free transmission resource forthe UE and configures the UE via indicating the grant-free transmissionresource through RRC signaling. The resource may include, but is notlimited to, time, frequency resource, reference signal information,MCS/TBS information, power control parameters, periodicity and offset ofthe resource, grant-free RNTI, repetition number K (K>=1) etc. After RRCsignaling, the UE has obtained the uplink transmission resources and canthen perform uplink transmission without any DCI signaling. After thefirst batch of data arrives at the UE, the UE can then perform initialgrant-free transmission of the first batch of data using the assignedgrant-free transmission resources. In some embodiments, the UE operatingin grant-free mode (“a grant-free UE”) may not monitor the DCI beforeperforming an initial grant-free transmission as it does not require aDCI activation to be able to perform grant-free transmission. A UEperforming the initial grant-free transmission of the data at time n mayonly start monitoring DCI at time n+t_a, where t_a is the time the UEstarts monitoring DCI after initial transmission. The unit of the timecan be a slot, a subframe, a mini-slot or any time unit measure. t_a canbe a predefined value or it can be configured by the network and sent tothe UE, e.g., via UE specific RRC signaling. If t_a is predefined, itcan be set as the earliest time that the UE is expected to receive a DCIfeedback after the initial grant-free transmission. In some embodiments,t_a=0 or 1, i.e., the UE may immediately check the DCI after the initialgrant-free transmission or check the DCI in the next slot. The DCI canbe UE specific and/or group-common DCI and can be used to transmitACK/NACK and/or an uplink grant. In some embodiments, the UE onlymonitors DCI or only monitors ACK/NACK after the K repetition isfinished. Assume the K repetitions of the grant-free transmission isfinished at time m and the UE may only start to monitor DCI or monitorACK/NACK at time m+t_b, where t_b can also be predefined or configuredin RRC signaling. The UE may optionally stop monitoring DCI at a timewindow after K repetition finishes, e.g., if the K repetition finishesat time m, the UE may stop monitoring the DCI at time m+t_c, where t_ccan be predefined or configured in RRC signaling.

If a UE assumes an ACK after not receiving any HARQ feedback or grantwithin a window T1 after K repetitions, the UE may stop furtherrepetition/retransmission until further signaling. In some embodiments,t_c is the same as Tl, i.e., the UE stops monitoring DCI at time m+Tl,so only one of them is predefined or configured in RRC signaling. Insome other embodiments, the UE assumes NACK after not receiving any HARQfeedback or grant within a window T1 and starts to perform autonomousretransmission/repetition of the TB until an ACK or grant is received oruntil a maximum number of retransmissions N or maximum retransmissiontime T2 (starting from initial grant-free transmission time n) isreceived as described earlier. The UE may stop monitoring DCI after n+T2is reached or at time t_c after the maximum number of retransmissions Nis reached. After stopping monitoring DCI for the transmission, the UEmay monitor the DCI again after t_a time of the next initial grant-freetransmission.

In some embodiments, the UE may monitor DCI all the time before or afterinitial grant-free transmission as there may be other functions (e.g.supported grant-based transmission) that requires DCI signaling. In someembodiments, the UE does not monitor DCI every TTi, but instead the UEmay only monitor DCI every T_m TTi, where T_m can be predefined orconfigured in RRC signaling. This can also apply to the case where theUE only starts monitoring DCI at time t_a after the initial grant-freetransmission. In general, the time and whether to monitor DCI can beconfigured for each UE, e.g. through RRC signaling.

EXAMPLES

In view of, and in addition to the above, the following examples aredisclosed.

Example 1

A method performed by a base station comprising: receiving a grant-freeuplink transmission from a user equipment (UE) on uplink resources;performing activity detection to obtain the MA signature used by the UEin the grant-free uplink transmission; attempting to decode data in thegrant-free uplink transmission; transmitting, in a downlinkacknowledgement channel, feedback comprising an ACK or a NACK; whereinan orthogonal sequence used to convey the feedback and/or atime-frequency location of the feedback is based on at least one of theMA signature and the uplink resources.

Example 2

The method of example 1, wherein the downlink acknowledgement channel isa PHICH-like channel.

Example 3

The method of example 1 or example 2, wherein the orthogonal sequenceused to convey the feedback is based on the MA signature, and thetime-frequency location of the feedback is based on the uplinkresources.

Example 4

The method of any one of examples 1 to 3, wherein feedback timing on thedownlink acknowledgement channel has a fixed relationship withgrant-free resource access timing used to send the grant-free uplinktransmission.

Example 5

The method of any one of examples 1 to 4, further comprising generatingthe feedback by performing operations comprising: obtaining one bitrepresenting the ACK or the NACK; repeating the bit to obtain aplurality of bits; modulating the plurality of bits to obtain symbols;and multiplying the symbols by the orthogonal sequence.

Example 6

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions to perform steps in accordance with amethod in any one of examples 1 to 5.

Example 7

A base station comprising: at least one antenna to receive a grant-freeuplink transmission from a user equipment (UE) on uplink resources; agrant-free transmission module to: (i) perform activity detection toobtain the MA signature used by the UE in the grant-free uplinktransmission; (ii) attempt to decode data in the grant-free uplinktransmission; and (iii) cause transmission of feedback comprising an ACKor a NACK, in a downlink acknowledgement channel; wherein an orthogonalsequence used to convey the feedback and/or a time-frequency location ofthe feedback is based on at least one of the MA signature and the uplinkresources.

Example 8

A method performed by a user equipment (UE) comprising: transmitting agrant-free uplink transmission to a base station on uplink resources,the grant-free uplink transmission utilizing an MA signature; receivingfeedback comprising an ACK or a NACK on a downlink acknowledgementchannel; wherein an orthogonal sequence used to convey the feedbackand/or a time-frequency location of the feedback is based on at leastone of the MA signature and the uplink resources.

Example 9

The method of example 8, wherein the downlink acknowledgement channel isa PHICH-like channel.

Example 10

The method of example 8 or example 9, wherein the orthogonal sequenceused to convey the feedback is based on the MA signature, and thetime-frequency location of the feedback is based on the uplinkresources.

Example 11

The method of any one of examples 8 to 10, wherein feedback timing onthe downlink acknowledgement channel has a fixed relationship withgrant-free resource access timing used to send the grant-free uplinktransmission.

Example 12

A user equipment (UE) comprising: a processor; and a computer readablestorage medium storing programming for execution by the processor, theprogramming including instructions to perform steps in accordance with amethod in any one of examples 8 to 11.

Example 13

A user equipment (UE) comprising: at least one antenna to transmit agrant-free uplink transmission to a base station on uplink resources,the grant-free uplink transmission utilizing an MA signature; a decoderto decode feedback corresponding to the grant-free uplink transmissionand received on a downlink acknowledgement channel, the feedbackcomprising an ACK or a NACK; wherein an orthogonal sequence used toconvey the feedback and/or a time-frequency location of the feedback isbased on at least one of the MA signature and the uplink resources.

Example 14

A method performed by a base station comprising: receiving a firstgrant-free uplink transmission from a first user equipment (UE);receiving a second grant-free uplink transmission from a second UE;transmitting a group ACK/NACK message having a payload that includes atleast an ACK or a NACK for the first grant-free uplink transmission andan ACK or a NACK for the second grant-free uplink transmission.

Example 15

The method of example 14, wherein the payload is a word comprising onebit indicating the ACK or the NACK for the first grant-free uplinktransmission and another bit indicating the ACK or the NACK for thesecond grant-free uplink transmission.

Example 16

The method of example 14, wherein the payload is a word comprising afirst pair of bits corresponding to the first grant-free uplinktransmission and a second pair of bits corresponding to the secondgrant-free uplink transmission, wherein each pair of bits includes a bitindicating whether activity detection was successful and another bitindicating whether data decoding was successful.

Example 17

The method of any one of examples 14 to 16, wherein one position indexin the payload corresponds to the first UE, and another position indexin the payload corresponds to the second UE.

Example 18

The method of example 14, wherein the payload comprises a plurality ofUE IDs, and wherein the presence of a UE ID in the payload indicates anACK for a UE corresponding to that UE ID.

Example 19

The method of any one of examples 14 to 18, wherein the payload includesACKs/NACKs for multiple HARQ process IDs.

Example 20

The method of any one of examples 14 to 19, wherein the payload is sentin a downlink control channel and is scrambled by a group ID.

Example 21

The method of any one of examples 14 to 19, wherein the payload is sentin a downlink data channel.

Example 22

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions to perform steps in accordance with amethod in any one of examples 14 to 21.

Example 23

A base station comprising: at least one antenna to receive a firstgrant-free uplink transmission from a first user equipment (UE) andreceive a second grant-free uplink transmission from a second UE; agrant-free transmission module to generate a group ACK/NACK messagehaving a payload that includes at least an ACK or a NACK for the firstgrant-free uplink transmission and an ACK or a NACK for the secondgrant-free uplink transmission.

Example 24

A method performed by a first user equipment (UE) comprising: sending afirst grant-free uplink transmission to a base station; receiving agroup ACK/NACK message having a payload that includes at least an ACK ora NACK for the first grant-free uplink transmission and an ACK or a NACKfor a second grant-free uplink transmission from a second UE.

Example 25

The method of example 24, wherein the payload is a word comprising onebit indicating the ACK or the NACK for the first grant-free uplinktransmission and another bit indicating the ACK or the NACK for thesecond grant-free uplink transmission.

Example 26

The method of example 24, wherein the payload is a word comprising afirst pair of bits corresponding to the first grant-free uplinktransmission and a second pair of bits corresponding to the secondgrant-free uplink transmission, wherein each pair of bits includes a bitindicating whether activity detection was successful and another bitindicating whether data decoding was successful.

Example 27

The method of any one of examples 24 to 26, wherein one position indexin the payload corresponds to the first UE, and another position indexin the payload corresponds to the second UE.

Example 28

The method of example 24, wherein the payload comprises a plurality ofUE IDs, and wherein the presence of a UE ID in the payload indicates anACK for a UE corresponding to that UE ID.

Example 29

The method of any one of examples 24 to 28, wherein the payload includesACKs/NACKs for multiple HARQ process IDs.

Example 30

The method of any one of examples 24 to 29, wherein the payload isreceived in a downlink control channel and is scrambled by a group ID.

Example 31

The method of any one of examples 24 to 29, wherein the payload isreceived in a downlink data channel.

Example 32

A user equipment (UE) comprising: a processor; and a computer readablestorage medium storing programming for execution by the processor, theprogramming including instructions to perform steps in accordance with amethod in any one of examples 24 to 31.

Example 33

A first user equipment (UE) comprising: at least one antenna to transmita first grant-free uplink transmission to a base station; a decoder todecode a group ACK/NACK message having a payload that includes at leastan ACK or a NACK for the first grant-free uplink transmission and an ACKor a NACK for a second grant-free uplink transmission from a second UE.

Example 34

A method performed by a base station comprising: receiving a firstgrant-free uplink transmission from a first user equipment (UE);receiving a second grant-free uplink transmission from a second UE;transmitting, to the first UE and to the second UE, a group ACK/NACKmessage having a payload that indicates an ACK or a NACK correspondingto the first grant-free uplink transmission and an ACK or a NACKcorresponding to the second grant-free uplink transmission.

Example 35

The method of example 34, wherein prior to transmitting the groupACK/NACK message, the base station attempts to decode first data in thefirst grant-free uplink transmission and second data in the secondgrant-free uplink transmission.

Example 36

The method of example 34 or 35, wherein the group ACK/NACK includes agrant that grants an uplink transmission to the first UE.

Example 37

The method of example 36, wherein the grant grants a retransmission ofdata sent in the first grant-free uplink transmission.

Example 38

The method of example 36, wherein the grant implicitly indicates theNACK corresponding to the first grant-free uplink transmission byscheduling a retransmission of data sent in the first grant-free uplinktransmission.

Example 39

The method of example 36, wherein the grant implicitly indicates the ACKcorresponding to the first grant-free uplink transmission by schedulinga transmission of new data.

Example 40

The method of any one of examples 34 to 39, wherein the first UE and thesecond UE are in a group having a group identifier (ID), and wherein thegroup ACK/NACK is associated with the group ID.

Example 41

The method of example 40, wherein the group ID is a radio networktemporary identifier (RNTI).

Example 42

The method of example 40 or 41, wherein the group ID is a function ofgrant-free resources at which the first grant-free uplink transmissionwas sent.

Example 43

The method of example 42, wherein the group ID is a function of a timeunit at which the first grant-free uplink transmission was sent.

Example 44

The method of example 43, wherein the time unit is a time slot.

Example 45

The method of example 43, wherein the group ID is also a function of theframe number at which the first grant-free uplink transmission was sent.

Example 46

The method of example 42, wherein the group ID is a function of afrequency location at which the first grant-free uplink transmission wassent.

Example 47

The method of example 42, wherein the group ID is a function of at leastone of a time unit and frequency location at which the first grant-freeuplink transmission was sent.

Example 48

The method of example 42, wherein the group ID is a function of at leastone of a subframe, slot number, and frame number at which the firstgrant-free uplink transmission was sent.

Example 49

The method of example 48, wherein the slot is a time slot.

Example 50

The method of any one of examples 40 to 49, wherein the group ID isconfigured in higher layer signaling.

Example 51

The method of example 50, further comprising signaling the group ID tothe first UE and to the second UE in radio resource control (RRC)signaling.

Example 52

The method of any one of examples 40 to 50, wherein the group ACK/NACKis transmitted in group-common downlink control information (DCI).

Example 53

The method of example 52, wherein the group-common DCI is sent in adownlink control channel in a search space defined by the group ID.

Example 54

The method of example 52 or 53, wherein a cyclic redundancy check (CRC)of the group-common DCI is masked by the group ID.

Example 55

The method of example 54, comprising the base station scrambling the CRCof the group-common DCI using the group ID.

Example 56

The method of any one of examples 34 to 55, wherein the payload is aword comprising one bit indicating the ACK or the NACK corresponding tothe first grant-free uplink transmission and another bit indicating theACK or the NACK corresponding to the second grant-free uplinktransmission.

Example 57

The method of any one of examples 34 to 55, wherein the payload is aword comprising a first pair of bits corresponding to the firstgrant-free uplink transmission and a second pair of bits correspondingto the second grant-free uplink transmission, wherein each pair of bitsincludes a bit indicating whether activity detection was successful andanother bit indicating whether data decoding was successful.

Example 58

The method of any one of examples 34 to 55, wherein one position in thepayload corresponds to the first UE, and another position in the payloadcorresponds to the second UE.

Example 59

The method of example 58, wherein the position corresponding to thefirst UE is based on an MA signature.

Example 60

The method of example 59, wherein the position corresponding to thefirst UE is known by the first UE based on the MA signature andgrant-free resources used by the first UE to send the first grant-freeuplink transmission.

Example 61

The method of example 58, wherein the position corresponding to thefirst UE is signalled to the first UE prior to the first UE sending thefirst grant-free uplink transmission.

Example 62

The method of example 61, wherein the position corresponding to thefirst UE is signalled using higher layering signaling.

Example 63

The method of example 62, wherein the higher layer signaling is RRCsignaling.

Example 64

The method of any one of examples 34 to 63, wherein the group ACK/NACKindicates an ACK for all received packets successfully decoded in oneTTI or one time slot or one subframe.

Example 65

The method of any one of examples 34 to 63, wherein the payloadcomprises a plurality of UE IDs, and wherein the presence of a UE ID inthe payload indicates an ACK for a UE corresponding to that UE ID.

Example 66

The method of any one of examples 34 to 63, wherein the payload includesACKs/NACKs for multiple HARQ process IDs.

Example 67

The method of example 66, wherein a HARQ process ID associated with datain the first grant-free uplink transmission is explicitly or implicitlyindicated in the first grant-free uplink transmission.

Example 68

The method of example 66, wherein data in the first grant-free uplinktransmission is associated with a HARQ process ID, and wherein aposition, in the payload, of the ACK or the NACK corresponding to thefirst grant-free uplink transmission is based on both a position indexcorresponding to the first UE and the HARQ process ID.

Example 69

The method of example 66, wherein the first UE is assigned multiplepositions in the payload, each one of the positions associated with arespective MA signature and/or HARQ process ID.

Example 70

The method of any one of examples 34 to 69, wherein the first grant-freeuplink transmission is one of a plurality of uplink repetitions of atransport block, and wherein the group ACK/NACK is used to terminate theuplink repetitions.

Example 71

The method of example 70, wherein the group ACK/NACK indicates an ACKcorresponding to the first grant-free uplink transmission in order toterminate the uplink repetitions.

Example 72

The method of any one of examples 34 to 71, wherein there is a fixedtiming relationship between: (i) uplink time-frequency resources atwhich the first grant-free uplink transmission and the second grant-freeuplink transmission were sent, and (ii) downlink time-frequencyresources on which the group ACK/NACK is sent.

Example 73

The method of any one of examples 34 to 71, wherein there is a fixedtiming relationship between: (i) a subframe or time unit during whichthe first grant-free uplink transmission and the second grant-freeuplink transmission were sent, and (ii) a subframe or time unit duringwhich the group ACK/NACK is sent.

Example 74

The method of any one of examples 34 to 71, wherein data in the firstgrant-free uplink transmission is associated with a HARQ process ID,wherein an indication of the HARQ process ID is present in downlinkcontrol information, and wherein the indication of the HARQ process IDis used by the first UE to identify that the data is being acknowledged.

Example 75

The method of example 34, wherein the payload is sent in a downlink datachannel.

Example 76

The method of example 75, further comprising transmitting downlinkcontrol information that indicates where to find the payload in thedownlink data channel.

Example 77

The method of example 34, wherein the payload includes a portioncorresponding to the first grant-free uplink transmission, wherein theportion has a location in the payload mapped to an MA signature utilizedby the first grant-free uplink transmission, and wherein the portionincludes at least one of: a scheduling grant for the first UE; timingadvanced (TA) information; a UE ID of the first UE; a temporary identityto be used for further communication between the first UE and the basestation; the ACK or the NACK corresponding to the first grant-freeuplink transmission.

Example 78

The method of example 57, wherein the first grant-free uplinktransmission carries first data, and wherein the method furthercomprises: when the first pair of bits indicates that activity detectionwas not successful, then receiving a retransmission of the first datafrom the first UE, the retransmission at a same redundancy version (RV)as the first grant-free uplink transmission.

Example 79

The method of example 57, wherein the first grant-free uplinktransmission carries first data, and wherein the method furthercomprises: when the first pair of bits indicates that activity detectionwas successful, but that data decoding was not successful, thenreceiving a retransmission of the first data from the first UE, theretransmission data at a different RV from the first grant-free uplinktransmission.

Example 80

A base station comprising: a receiver to receive a first grant-freeuplink transmission from a first user equipment (UE), and to receive asecond grant-free uplink transmission from a second UE; a grant-freetransmission module to generate a group ACK/NACK message having apayload that indicates an ACK or a NACK corresponding to the firstgrant-free uplink transmission and an ACK or a NACK corresponding to thesecond grant-free uplink transmission.

Example 81

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions that, when executed by the processor,cause the base station to perform the method of any one of examples 34to 79.

Example 82

A method performed by a user equipment (UE) comprising: transmitting afirst grant-free uplink transmission to a base station; receiving agroup ACK/NACK message having a payload that indicates an ACK or a NACKcorresponding to the first grant-free uplink transmission and an ACK ora NACK corresponding to a second grant-free uplink transmission from asecond UE.

Example 83

The method of example 82, wherein the first UE and the second UE are ina group having a group identifier (ID), and wherein the group ACK/NACKis associated with the group ID.

Example 84

The method of example 83, wherein the group ID is a radio networktemporary identifier (RNTI).

Example 85

The method of example 83 or 84, wherein the group ID is a function ofgrant-free resources at which the first grant-free uplink transmissionis sent.

Example 86

The method of example 85, wherein the group ID is a function of a timeunit at which the first grant-free uplink transmission is sent.

Example 87

The method of example 86, wherein the time unit is a time slot.

Example 88

The method of example 86 or 87, wherein the group ID is also a functionof the frame number at which the first grant-free uplink transmission issent.

Example 89

The method of example 85, wherein the group ID is a function of afrequency location at which the first grant-free uplink transmission issent.

Example 90

The method of example 85, wherein the group ID is a function of at leastone of a time unit and frequency location at which the first grant-freeuplink transmission is sent.

Example 91

The method of example 85, wherein the group ID is a function of at leastone of a subframe, slot, and frame number at which the first grant-freeuplink transmission is sent.

Example 92

The method of example 91, wherein the slot is a time slot.

Example 93

The method of any one of examples 83 to 92, wherein the group ID isconfigured in higher layer signaling.

Example 94

The method of example 93, further comprising receiving, from the basestation, an indication of the group ID in radio resource control (RRC)signaling.

Example 95

The method of any one of examples 83 to 94, wherein the group ACK/NACKis received in group-common downlink control information (DCI).

Example 96

The method of example 95, wherein the group-common DCI is received in adownlink control channel in a search space defined by the group ID.

Example 97

The method of example 95 or 96, wherein a cyclic redundancy check (CRC)of the group-common DCI is masked by the group ID.

Example 98

The method of example 97, further comprising unscrambling the CRC of thegroup-common DCI using the group ID.

Example 99

The method of any one of examples 82 to 98, wherein the payload is aword comprising one bit indicating the ACK or the NACK corresponding tothe first grant-free uplink transmission and another bit indicating theACK or the NACK corresponding to the second grant-free uplinktransmission.

Example 100

The method of any one of examples 82 to 98, wherein the payload is aword comprising a first pair of bits corresponding to the firstgrant-free uplink transmission and a second pair of bits correspondingto the second grant-free uplink transmission, wherein each pair of bitsincludes a bit indicating whether activity detection was successful andanother bit indicating whether data decoding was successful.

Example 101

The method of any one of examples 82 to 98, wherein one position in thepayload corresponds to the first UE, and another position in the payloadcorresponds to the second UE.

Example 102

The method of example 101, wherein the position corresponding to thefirst UE is based on an MA signature.

Example 103

The method of example 102, wherein the position corresponding to thefirst UE is known by the first UE based on the MA signature andgrant-free resources used by the first UE to send the first grant-freeuplink transmission.

Example 104

The method of example 101, wherein the position corresponding to thefirst UE is signalled to the first UE prior to the first UE sending thefirst grant-free uplink transmission.

Example 105

The method of example 104, wherein the position corresponding to thefirst UE is signalled using higher layering signaling.

Example 106

The method of example 105, wherein the higher layer signaling is RRCsignaling.

Example 107

The method of any one of examples 82 to 106, wherein the group ACK/NACKindicates an ACK for all received packets successfully decoded in oneTTI or one time slot or one subframe.

Example 108

The method of any one of examples 82 to 107, wherein the payloadcomprises a plurality of UE IDs, and wherein the presence of a UE ID inthe payload indicates an ACK for a UE corresponding to that UE ID.

Example 109

The method of example 82, wherein the payload includes ACKs/NACKs formultiple HARQ process IDs.

Example 110

The method of example 109, wherein a HARQ process ID is associated withdata in the first grant-free uplink transmission, and wherein the HARQprocess ID is explicitly or implicitly indicated in the first grant-freeuplink transmission.

Example 111

The method of example 109, wherein a HARQ process ID is associated withdata in the first grant-free uplink transmission, and wherein aposition, in the payload, of the ACK or the NACK corresponding to thefirst grant-free uplink transmission is based on both a position indexcorresponding to the first UE and the HARQ process ID.

Example 112

The method of example 109, wherein the first UE is assigned multiplepositions in the payload, each one of the positions associated with arespective MA signature and/or HARQ process ID.

Example 113

The method of any one of examples 82 to 112, wherein the firstgrant-free uplink transmission is one of a plurality of uplinkrepetitions of a transport block, and wherein the group ACK/NACK is usedto terminate the uplink repetitions.

Example 114

The method of example 113, wherein the group ACK/NACK indicates an ACKcorresponding to the first grant-free uplink transmission in order toterminate the uplink repetitions.

Example 115

The method of any one of examples 82 to 114, wherein there is a fixedtiming relationship between: (i) uplink time-frequency resources atwhich the first grant-free uplink transmission is sent, and (ii)downlink time-frequency resources on which the group ACK/NACK isreceived.

Example 116

The method of any one of examples 82 to 114, wherein there is a fixedtiming relationship between: (i) a subframe or time unit during whichthe first grant-free uplink transmission is sent, and (ii) a subframe ortime unit during which the group ACK/NACK is received.

Example 117

The method of any one of examples 82 to 116, wherein a HARQ process IDis associated with data in the first grant-free uplink transmission, anindication of the HARQ process ID is present in downlink controlinformation, and the indication of the HARQ process ID is used by thefirst UE to identify that the data is being acknowledged.

Example 118

The method of any one of examples 82 to 117, wherein the payload isreceived in a downlink data channel.

Example 119

The method of example 118, further comprising receiving downlink controlinformation that indicates where to find the payload in the downlinkdata channel.

Example 120

The method of any one of examples 82 to 119, wherein the payloadincludes a portion corresponding to the first grant-free uplinktransmission, wherein the portion has a location in the payload mappedto an MA signature utilized by the first grant-free uplink transmission,and wherein the portion includes at least one of: a scheduling grant forthe first UE; timing advanced (TA) information; a UE ID of the first UE;a temporary identity to be used for further communication between thefirst UE and the base station; the ACK or the NACK corresponding to thefirst grant-free uplink transmission.

Example 121

The method of example 95, further comprising decoding the group-commonDCI, including performing a CRC check using the group ID.

Example 122

The method of example 121, wherein the group ID is a RNTI.

Example 123

The method of example 95, further comprising searching a search space ina downlink control channel using the group ID to obtain the group-commonDCI.

Example 124

The method of example 123, wherein the search space that is searched isa function of the uplink resources used to transmit the first grant-freeuplink transmission.

Example 125

The method of example 100, further comprising: when the first pair ofbits indicates that activity detection was not successful, thenretransmitting data from the first grant-free uplink transmission at asame redundancy version (RV) as the first grant-free uplinktransmission.

Example 126

The method of example 100, further comprising: when the first pair ofbits indicates that activity detection was successful, but that datadecoding was not successful, then retransmitting data from the firstgrant-free uplink transmission at a different RV from the firstgrant-free uplink transmission.

Example 127

The method of any one of examples 82 to 126, wherein the group ACK/NACKincludes a grant that grants an uplink transmission to the UE.

Example 128

The method of example 127, wherein the grant grants a retransmission ofdata sent in the first grant-free uplink transmission.

Example 129

A user equipment (UE) comprising: a transmitter to transmit a firstgrant-free uplink transmission to a base station; a receiver to receivea group ACK/NACK message having a payload that indicates an ACK or aNACK corresponding to the first grant-free uplink transmission and anACK or a NACK corresponding to a second grant-free uplink transmissionfrom a second UE.

Example 130

A UE comprising: a processor; and a computer readable storage mediumstoring programming for execution by the processor, the programmingincluding instructions that, when executed by the processor, cause theUE to perform the method of any one of examples 82 to 128.

Example 131

A method performed by a base station comprising: receiving a grant-freeuplink transmission from a user equipment (UE), the grant-free uplinktransmission carrying data corresponding to a first transport block;transmitting a grant to the UE, wherein the grant schedules aretransmission of the first transport block when decoding of the firsttransport block fails or schedules a transmission of a second transportblock when decoding of the first transport block is successful.

Example 132

The method of example 131, wherein the grant does not include anexplicit ACK or an explicit NACK for the first transport block.

Example 133

The method of example 131 or 132, wherein the grant is sent in downlinkcontrol information (DCI).

Example 134

The method of any one of examples 131 to 133, wherein the grant is sentas part of a group ACK/NACK.

Example 135

The method of any one of examples 131 to 134, wherein prior totransmitting the grant, the base station attempts to decode the firsttransport block based on the data in the grant-free uplink transmission.

Example 136

The method of any one of examples 131 to 135, wherein the grantimplicitly indicates a NACK for the first transport block by schedulingthe retransmission of the first transport block.

Example 137

The method of any one of examples 131 to 135, wherein the grantimplicitly indicates an ACK for the first transport block by schedulingthe transmission of the second transport block.

Example 138

The method of any one of examples 131 to 137, wherein the grant includesa HARQ process ID corresponding to the first transport block.

Example 139

The method of any one of examples 131 to 138, wherein the grant-freeuplink transmission is one of a plurality of uplink repetitions of thefirst transport block, and wherein the grant terminates the uplinkrepetitions.

Example 140

A base station comprising: a receiver to receive a grant-free uplinktransmission from a user equipment (UE), the grant-free uplinktransmission carrying data corresponding to a first transport block; agrant-free transmission module to generate a grant for the UE; whereinthe grant schedules a retransmission of the first transport block whendecoding of the first transport block fails or schedules a transmissionof a second transport block when decoding of the first transport blockis successful.

Example 141

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions that, when executed by the processor,cause the base station to perform the method of any one of examples 131to 139.

Example 142

A method performed by a user equipment (UE) comprising: transmitting agrant-free uplink transmission to a base station, the grant-free uplinktransmission carrying data corresponding to a first transport block;receiving a grant from the base station, wherein the grant schedules aretransmission of the first transport block when decoding of the firsttransport block failed at the base station or schedules a transmissionof a second transport block when decoding of the first transport blockwas successful at the base station; transmitting an uplink transmissionaccording to the grant.

Example 143

The method of example 142, wherein in response to transmitting thegrant-free uplink transmission: an explicit ACK or an explicit NACK forthe first transport block is not received by the UE.

Example 144

The method of example 142 or 143, wherein the grant is received indownlink control information (DCI).

Example 145

The method of any one of examples 142 to 144, wherein the grant isreceived as part of a group ACK/NACK.

Example 146

The method of any one of examples 142 to 145, wherein the grantimplicitly indicates a NACK for the first transport block by schedulingthe retransmission of the first transport block.

Example 147

The method of any one of examples 142 to 145, wherein the grantimplicitly indicates an ACK for the first transport block by schedulingthe transmission of the second transport block.

Example 148

The method of any one of examples 142 to 147, wherein the grant includesa HARQ process ID corresponding to the first transport block.

Example 149

The method of any one of examples 142 to 148, wherein the grant-freeuplink transmission is one of a plurality of uplink repetitions of thefirst transport block, and wherein the grant terminates the uplinkrepetitions.

Example 150

A user equipment (UE) comprising: a grant-free transmission module togenerate a message to be transmitted to a base station via a grant-freeuplink transmission, the message carrying data corresponding to a firsttransport block; a receiver to receive a grant from the base station,wherein the grant schedules a retransmission of the first transportblock when decoding of the first transport block failed at the basestation or schedules a transmission of a second transport block whendecoding of the first transport block was successful at the basestation; a transmitter to transmit an uplink transmission according tothe grant.

Example 151

A UE comprising: a processor; and a computer readable storage mediumstoring programming for execution by the processor, the programmingincluding instructions that, when executed by the processor, cause theUE to perform the method of any one of examples 142 to 149.

Example 152

A method performed by a base station comprising: receiving a grant-freeuplink transmission from a user equipment (UE) on uplink resources;transmitting, in a downlink acknowledgement channel, feedbackcorresponding to the grant-free uplink transmission, the feedbackcomprising an ACK or a NACK; wherein an orthogonal sequence used toconvey the feedback and/or a time-frequency location of the feedback isbased on at least one of the MA signature and the uplink resources.

Example 153

The method of example 152, wherein the orthogonal sequence used toconvey the feedback is based on the MA signature, and the time-frequencylocation of the feedback is based on the uplink resources.

Example 154

The method of example 152 or 153, wherein feedback timing on thedownlink acknowledgement channel has a fixed relationship withgrant-free resource access timing used to send the grant-free uplinktransmission.

Example 155

The method of any one of examples 152 to 154, further comprisinggenerating the feedback by performing operations comprising: obtainingone bit representing the ACK or the NACK repeating the bit to obtain aplurality of bits; modulating the plurality of bits to obtain symbols;and multiplying the symbols by the orthogonal sequence.

Example 156

The method of any one of examples 152 to 155, wherein the downlinkacknowledgement channel is a PHICH-like channel.

Example 157

A base station comprising: a receiver to receive a grant-free uplinktransmission from a user equipment (UE) on uplink resources; agrant-free transmission module to generate, for transmission in adownlink acknowledgement channel, feedback corresponding to thegrant-free uplink transmission, the feedback comprising an ACK or aNACK; wherein an orthogonal sequence used to convey the feedback and/ora time-frequency location of the feedback is based on at least one ofthe MA signature and the uplink resources.

Example 158

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions that, when executed by the processor,cause the base station to perform the method of any one of examples 152to 156.

Example 159

A method performed by a user equipment (UE) comprising: transmitting agrant-free uplink transmission to a base station on uplink resources,the grant-free uplink transmission utilizing an MA signature; receiving,on a downlink acknowledgement channel, feedback corresponding to thegrant-free uplink transmission, the feedback comprising an ACK or aNACK; wherein an orthogonal sequence used to convey the feedback and/ora time-frequency location of the feedback is based on at least one ofthe MA signature and the uplink resources.

Example 160

The method of example 159, wherein the orthogonal sequence used toconvey the feedback is based on the MA signature, and the time-frequencylocation of the feedback is based on the uplink resources.

Example 161

The method of example 159 or 160, wherein feedback timing on thedownlink acknowledgement channel has a fixed relationship withgrant-free resource access timing used to send the grant-free uplinktransmission.

Example 162

The method of any one of examples 159 to 161, wherein the downlinkacknowledgement channel is a PHICH-like channel.

Example 163

A user equipment (UE) comprising: a transmitter to transmit a grant-freeuplink transmission to a base station on uplink resources, thegrant-free uplink transmission utilizing an MA signature; a decoder todecode feedback corresponding to the grant-free uplink transmission andreceived on a downlink acknowledgement channel, the feedback comprisingan ACK or a NACK; wherein an orthogonal sequence used to convey thefeedback and/or a time-frequency location of the feedback is based on atleast one of the MA signature and the uplink resources.

Example 164

A UE comprising: a processor; and a computer readable storage mediumstoring programming for execution by the processor, the programmingincluding instructions that, when executed by the processor, cause theUE to perform the method of any one of examples 159 to 162.

Example 165

A method performed by a base station comprising: receiving, on uplinktime-frequency resources, a grant-free uplink transmission from a userequipment (UE); transmitting, in downlink control information (DCI),feedback corresponding to the grant-free uplink transmission; wherein aCRC of the DCI is masked using an ID, and wherein the ID is a functionof the uplink time-frequency resources on which the grant-free uplinktransmission was received.

Example 166

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions that, when executed by the processor,cause the base station to perform the method of example 165.

Example 167

A method performed by UE comprising: transmitting, on uplinktime-frequency resources, a grant-free uplink transmission to a basestation; receiving, in downlink control information (DCI), feedbackcorresponding to the grant-free uplink transmission; wherein a CRC ofthe DCI is masked using an ID, and wherein the ID is a function of theuplink time-frequency resources on which the grant-free uplinktransmission was sent.

Example 168

A UE comprising: a processor; and a computer readable storage mediumstoring programming for execution by the processor, the programmingincluding instructions that, when executed by the processor, cause theUE to perform the method of example 167.

Example 169

A method performed by a base station comprising: transmitting, to a userequipment, an indication of a modulation and coding (MCS) scheme to beused by the UE for a grant-free uplink transmission; receiving thegrant-free uplink transmission from the UE, the grant-free uplinktransmission carrying data having the MCS.

Example 170

The method of example 169, wherein the indication is transmitted inradio resource control (RRC) signaling.

Example 171

The method of example 169 or 170, wherein the indication indicates anMCS hopping pattern to be used by the UE for a plurality of grant-freeuplink transmissions.

Example 172

The method of example 171, wherein the MCS hopping pattern indicatesthat a first grant-free uplink transmission is to use a first MCS and asecond grant-free uplink transmission is to use a second MCS, whereinthe second MCS is lower than the first MCS.

Example 173

The method of example 172, wherein the first grant-free uplinktransmission is a first repetition of a transport block and the secondgrant-free uplink transmission is a second repetition of the transportblock.

Example 174

A base station comprising: a transmitter to transmit, to a userequipment, an indication of a modulation and coding (MCS) scheme to beused by the UE for a grant-free uplink transmission; a receiver toreceive the grant-free uplink transmission from the UE, the grant-freeuplink transmission carrying data having the MCS.

Example 175

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions that, when executed by the processor,cause the base station to perform the method of any one of examples 169to 173.

Example 176

A method performed by a user equipment (UE) comprising: receiving, froma base station, an indication of a modulation and coding (MCS) scheme tobe used by the UE for a grant-free uplink transmission; transmitting thegrant-free uplink transmission to the base station, the grant-freeuplink transmission carrying data having the MCS.

Example 177

The method of example 176, wherein the indication is received in radioresource control (RRC) signaling.

Example 178

The method of example 176 or 177, wherein the indication indicates anMCS hopping pattern to be used by the UE for a plurality of grant-freeuplink transmissions.

Example 179

The method of example 178, wherein the MCS hopping pattern indicatesthat a first grant-free uplink transmission is to use a first MCS and asecond grant-free uplink transmission is to use a second MCS, whereinthe second MCS is lower than the first MCS.

Example 180

The method of example 179, wherein the first grant-free uplinktransmission is a first repetition of a transport block and the secondgrant-free uplink transmission is a second repetition of the transportblock.

Example 181

A user equipment (UE) comprising: a receiver to receive, from a basestation, an indication of a modulation and coding (MCS) scheme to beused by the UE for a grant-free uplink transmission; a transmitter totransmit the grant-free uplink transmission to the base station, thegrant-free uplink transmission carrying data having the MCS.

Example 182

A UE comprising: a processor; and a computer readable storage mediumstoring programming for execution by the processor, the programmingincluding instructions that, when executed by the processor, cause theUE to perform the method of any one of examples 176 to 180.

Example 183

A method performed by a base station, the method comprising: receivingtwo uplink transmissions from a user equipment (UE) in a same time slot,the two uplink transmissions comprising a first uplink transmissionreceived on first uplink time-frequency resources and a second uplinktransmission received on second uplink time-frequency resources.

Example 184

The method of example 183, wherein the first uplink transmission carriesa first transport block corresponding to a first HARQ process, and thesecond uplink transmission carries a second transport blockcorresponding to a second HARQ process.

Example 185

The method of example 184, wherein a HARQ process ID of the first HARQprocess is implicitly identified by the first uplink time-frequencyresources on which the first uplink transmission is received.

Example 186

A base station comprising: a receiver to receive two uplinktransmissions from a user equipment (UE) in a same time slot, the twouplink transmissions comprising a first uplink transmission received onfirst uplink time-frequency resources and a second uplink transmissionreceived on second uplink time-frequency resources.

Example 187

A base station comprising: a processor; and a computer readable storagemedium storing programming for execution by the processor, theprogramming including instructions that, when executed by the processor,cause the base station to perform the method of any one of examples 183to 185.

Example 188

A method performed by a user equipment (UE), the method comprising:transmitting two uplink transmissions to a base station in a same timeslot, the two uplink transmissions comprising a first uplinktransmission sent on first uplink time-frequency resources and a seconduplink transmission sent on second uplink time-frequency resources.

Example 189

The method of example 188, wherein the first uplink transmission carriesa first transport block corresponding to a first HARQ process, and thesecond uplink transmission carries a second transport blockcorresponding to a second HARQ process.

Example 190

The method of example 189, wherein a HARQ process ID of the first HARQprocess is implicitly identified by the first uplink time-frequencyresources on which the first uplink transmission is sent.

Example 191

A user equipment (UE) comprising: a transmitter to transmit two uplinktransmissions to a base station in a same time slot, the two uplinktransmissions comprising a first uplink transmission sent on firstuplink time-frequency resources and a second uplink transmission sent onsecond uplink time-frequency resources.

Example 192

A UE comprising: a processor; and a computer readable storage mediumstoring programming for execution by the processor, the programmingincluding instructions that, when executed by the processor, cause theUE to perform the method of any one of examples 188 to 190.

Example 193

A method performed by a base station comprising: receiving a firstgrant-free uplink transmission from a first user equipment (UE);receiving a second grant-free uplink transmission from a second UE;transmitting, to the first UE and to the second UE, a group ACK/NACKmessage, wherein the first UE and the second UE are in a group having agroup identifier (ID), wherein the group ACK/NACK is associated with thegroup ID, and wherein the group ID is a function of at least one of asubframe, slot number, and frame number at which the first grant-freeuplink transmission was sent.

Example 194

A method performed by a first UE comprising: transmitting a firstgrant-free uplink transmission to a base station; receiving a groupACK/NACK message directed to the first UE and a second UE, wherein thefirst UE and the second UE are in a group having a group identifier(ID), wherein the group ACK/NACK is associated with the group ID, andwherein the group ID is a function of at least one of a subframe, slotnumber, and frame number at which the first grant-free uplinktransmission was sent.

Example 195

A method performed by a base station comprising: receiving a firstgrant-free uplink transmission from a first user equipment (UE);receiving a second grant-free uplink transmission from a second UE;transmitting, to the first UE and to the second UE, a group ACK/NACKmessage indicating an ACK or a NACK corresponding to the firstgrant-free uplink transmission and an ACK or a NACK corresponding to thesecond grant-free uplink transmission.

Example 196

The method of example 195, wherein the first UE and the second UE are ina group having a group identifier (ID), wherein the group ACK/NACK isassociated with the group ID, and wherein the group ID is a function ofgrant-free resources at which the first grant-free uplink transmissionwas sent.

Example 197

The method of example 195, wherein the first UE and the second UE are ina group having a group ID, wherein the group ACK/NACK is associated withthe group ID, wherein the group ACK/NACK is transmitted in group-commondownlink control information (DCI), and wherein a cyclic redundancycheck (CRC) of the group-common DCI is masked by the group ID.

Example 198

The method of example 197, wherein the group ID is a function of atleast one of a time unit and frequency location at which the firstgrant-free uplink transmission was sent.

Example 199

The method of example 197 or 198, wherein the group ID is a radionetwork temporary identifier (RNTI) and is signaled to the first UE inradio resource control (RRC) signaling.

Example 200

The method of any one of examples 195 to 199, wherein the group ACK/NACKmessage has a payload that indicates the ACK or NACK, wherein thepayload comprises a first bit corresponding to the first grant-freeuplink transmission and a second bit corresponding to the secondgrant-free uplink transmission, wherein each bit indicates whetheractivity detection was successful or whether data decoding wassuccessful.

Example 201

The method of example 200, wherein a position of the first and secondbits in the payload corresponds to at least one of an MA signature and aHARQ process ID of the first and second grant-free uplink transmissions.

Example 202

The method of example 200, wherein a position of the first bit in thepayload is signalled to the first UE, using radio resource control (RRC)signaling, prior to the first UE sending the first grant-free uplinktransmission.

Example 203

A base station comprising: a receiver to receive a first grant-freeuplink transmission from a first user equipment (UE), and to receive asecond grant-free uplink transmission from a second UE; a grant-freetransmission module to generate a group ACK/NACK message that indicatesan ACK or a NACK corresponding to the first grant-free uplinktransmission and an ACK or a NACK corresponding to the second grant-freeuplink transmission.

Example 204

The base station of example 203, wherein the first UE and the second UEare in a group having a group identifier (ID), wherein the groupACK/NACK is associated with the group ID, and wherein the group ID is afunction of grant-free resources at which the first grant-free uplinktransmission was sent.

Example 205

The base station of example 203, wherein the first UE and the second UEare in a group having a group ID, wherein the group ACK/NACK isassociated with the group ID, wherein the base station is to transmitthe group ACK/NACK in group-common downlink control information (DCI)and to mask a cyclic redundancy check (CRC) of the group-common DCI bythe group ID.

Example 206

The base station of example 205, wherein the group ID is a function ofat least one of a time unit and frequency location at which the firstgrant-free uplink transmission was sent.

Example 207

The base station of any one of examples 203 to 206, wherein the groupACK/NACK message has a payload that indicates the ACK or NACK, whereinthe payload comprises a first bit corresponding to the first grant-freeuplink transmission and a second bit corresponding to the secondgrant-free uplink transmission, wherein each bit indicates whetheractivity detection was successful or whether data decoding wassuccessful.

Example 208

The base station of example 207, wherein a position of the first andsecond bits in the payload corresponds to at least one of an MAsignature and a HARQ process ID of the first and second grant-freeuplink transmissions.

Example 209

The base station of example 207 or 208, wherein the base station is tosignal, to the first UE, a position of the first bit in the payload,using radio resource control (RRC) signaling, prior to the first UEsending the first grant-free uplink transmission.

Example 210

A method performed by a first user equipment (UE) comprising:transmitting a first grant-free uplink transmission to a base station;receiving a group ACK/NACK message indicating an ACK or a NACKcorresponding to the first grant-free uplink transmission and an ACK ora NACK corresponding to a second grant-free uplink transmission from asecond UE.

Example 211

The method of example 210, wherein the first UE and the second UE are ina group having a group identifier (ID), wherein the group ACK/NACK isassociated with the group ID, and wherein the group ID is a function ofgrant-free resources at which the first grant-free uplink transmissionis sent.

Example 212

The method of example 210, wherein the first UE and the second UE are ina group having a group ID, wherein the group ACK/NACK is associated withthe group ID, wherein the group ACK/NACK is received in group-commondownlink control information (DCI), and wherein a cyclic redundancycheck (CRC) of the group-common DCI is masked by the group ID.

Example 213

The method of example 211 or 212, wherein the group ID is a function ofat least one of a time unit and frequency location at which the firstgrant-free uplink transmission is sent.

Example 214

The method of any one of examples 211 to 213, wherein the group ID is aradio network temporary identifier (RNTI) and is signaled to the firstUE in radio resource control (RRC) signaling.

Example 215

The method of any one examples 211 to 214, wherein the group ACK/NACKmessage has a payload that indicates the ACK or NACK, wherein thepayload comprises a first bit corresponding to the first grant-freeuplink transmission and a second bit corresponding to the secondgrant-free uplink transmission, wherein each bit indicates whetheractivity detection was successful or whether data decoding wassuccessful.

Example 216

The method of example 215, wherein a position of the first and secondbits in the payload corresponds to at least one of an MA signature and aHARQ process ID of the first and second grant-free uplink transmissions.

Example 217

The method of example 215, wherein a position of the first bit in thepayload is signalled to the first UE, using radio resource control (RRC)signaling, prior to the first UE sending the first grant-free uplinktransmission.

Example 218

A first user equipment (UE) comprising: a transmitter to transmit afirst grant-free uplink transmission to a base station; a receiver toreceive a group ACK/NACK message that indicates an ACK or a NACKcorresponding to the first grant-free uplink transmission and an ACK ora NACK corresponding to a second grant-free uplink transmission from asecond UE.

Example 219

The first UE of example 218, wherein the first UE and the second UE arein a group having a group identifier (ID), wherein the group ACK/NACK isassociated with the group ID, and wherein the group ID is a function ofgrant-free resources at which the first grant-free uplink transmissionis sent.

Example 220

The first UE of example 218, wherein the first UE and the second UE arein a group having a group ID, wherein the group ACK/NACK is associatedwith the group ID, wherein the receiver is to receive the group ACK/NACKin group-common downlink control information (DCI), and wherein a cyclicredundancy check (CRC) of the group-common DCI is masked by the groupID.

Example 221

The first UE of example 219 or 220, wherein the group ID is a functionof at least one of a time unit and frequency location at which the firstgrant-free uplink transmission is sent.

Example 222

The first UE of any one of examples 218 to 221, wherein the groupACK/NACK message has a payload that indicates the ACK or NACK, whereinthe payload comprises a first bit corresponding to the first grant-freeuplink transmission and a second bit corresponding to the secondgrant-free uplink transmission, wherein each bit indicates whetheractivity detection was successful or whether data decoding wassuccessful.

Example 223

The first UE of example 222, wherein a position of the first and secondbits in the payload corresponds to at least one of an MA signature and aHARQ process ID of the first and second grant-free uplink transmissions.

Example 224

The first UE of example 222, wherein a position of the first bit in thepayload is signalled to the first UE, using radio resource control (RRC)signaling, prior to the first UE sending the first grant-free uplinktransmission.

CONCLUSION

Although the present invention has been described with reference tospecific features and embodiments thereof, various modifications andcombinations can be made thereto without departing from the invention.The description and drawings are, accordingly, to be regarded simply asan illustration of some embodiments of the invention as defined by theappended claims, and are contemplated to cover any and allmodifications, variations, combinations or equivalents that fall withinthe scope of the present invention. Therefore, although the presentinvention and its advantages have been described in detail, variouschanges, substitutions and alterations can be made herein withoutdeparting from the invention as defined by the appended claims.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

Moreover, any module, component, or device exemplified herein thatexecutes instructions may include or otherwise have access to anon-transitory computer/processor readable storage medium or media forstorage of information, such as computer/processor readableinstructions, data structures, program modules, and/or other data. Anon-exhaustive list of examples of non-transitory computer/processorreadable storage media includes magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, optical diskssuch as compact disc read-only memory (CD-ROM), digital video discs ordigital versatile disc (DVDs), Blu-ray Disc™, or other optical storage,volatile and non-volatile, removable and non-removable media implementedin any method or technology, random-access memory (RAM), read-onlymemory (ROM), electrically erasable programmable read-only memory(EEPROM), flash memory or other memory technology. Any suchnon-transitory computer/processor storage media may be part of a deviceor accessible or connectable thereto. Any application or module hereindescribed may be implemented using computer/processorreadable/executable instructions that may be stored or otherwise held bysuch non-transitory computer/processor readable storage media.

1. A method performed by a base station comprising: receiving a firstgrant-free uplink transmission from a first user equipment (UE);receiving a second grant-free uplink transmission from a second UE;transmitting, to the first UE and to the second UE, a group ACK/NACKmessage indicating an ACK or a NACK corresponding to the firstgrant-free uplink transmission and an ACK or a NACK corresponding to thesecond grant-free uplink transmission.
 2. The method of claim 1, whereinthe first UE and the second UE are in a group having a group identifier(ID), wherein the group ACK/NACK is associated with the group ID, andwherein the group ID is a function of grant-free resources at which thefirst grant-free uplink transmission was sent.
 3. The method of claim 1,wherein the first UE and the second UE are in a group having a group ID,wherein the group ACK/NACK is associated with the group ID, wherein thegroup ACK/NACK is transmitted in group-common downlink controlinformation (DCI), and wherein a cyclic redundancy check (CRC) of thegroup-common DCI is masked by the group ID.
 4. The method of claim 3,wherein the group ID is a function of at least one of a time unit andfrequency location at which the first grant-free uplink transmission wassent.
 5. The method of claim 3, wherein the group ID is a radio networktemporary identifier (RNTI) and is signaled to the first UE in radioresource control (RRC) signaling.
 6. The method of claim 1, wherein thegroup ACK/NACK message has a payload that indicates the ACK or NACK,wherein the payload comprises a first bit corresponding to the firstgrant-free uplink transmission and a second bit corresponding to thesecond grant-free uplink transmission, wherein each bit indicateswhether activity detection was successful or whether data decoding wassuccessful.
 7. The method of claim 6, wherein a position of the firstand second bits in the payload corresponds to at least one of an MAsignature and a HARQ process ID of the first and second grant-freeuplink transmissions.
 8. The method of claim 6, wherein a position ofthe first bit in the payload is signalled to the first UE, using radioresource control (RRC) signaling, prior to the first UE sending thefirst grant-free uplink transmission.
 9. A base station comprising: areceiver to receive a first grant-free uplink transmission from a firstuser equipment (UE), and to receive a second grant-free uplinktransmission from a second UE; a grant-free transmission module togenerate a group ACK/NACK message that indicates an ACK or a NACKcorresponding to the first grant-free uplink transmission and an ACK ora NACK corresponding to the second grant-free uplink transmission. 10.The base station of claim 9, wherein the first UE and the second UE arein a group having a group identifier (ID), wherein the group ACK/NACK isassociated with the group ID, and wherein the group ID is a function ofgrant-free resources at which the first grant-free uplink transmissionwas sent.
 11. The base station of claim 9, wherein the first UE and thesecond UE are in a group having a group ID, wherein the group ACK/NACKis associated with the group ID, wherein the base station is to transmitthe group ACK/NACK in group-common downlink control information (DCI)and to mask a cyclic redundancy check (CRC) of the group-common DCI bythe group ID.
 12. The base station of claim 11, wherein the group ID isa function of at least one of a time unit and frequency location atwhich the first grant-free uplink transmission was sent.
 13. The basestation of claim 9, wherein the group ACK/NACK message has a payloadthat indicates the ACK or NACK, wherein the payload comprises a firstbit corresponding to the first grant-free uplink transmission and asecond bit corresponding to the second grant-free uplink transmission,wherein each bit indicates whether activity detection was successful orwhether data decoding was successful.
 14. The base station of claim 13,wherein a position of the first and second bits in the payloadcorresponds to at least one of an MA signature and a HARQ process ID ofthe first and second grant-free uplink transmissions.
 15. The basestation of claim 13, wherein the base station is to signal, to the firstUE, a position of the first bit in the payload, using radio resourcecontrol (RRC) signaling, prior to the first UE sending the firstgrant-free uplink transmission.
 16. A method performed by a first userequipment (UE) comprising: transmitting a first grant-free uplinktransmission to a base station; receiving a group ACK/NACK messageindicating an ACK or a NACK corresponding to the first grant-free uplinktransmission and an ACK or a NACK corresponding to a second grant-freeuplink transmission from a second UE.
 17. The method of claim 16,wherein the first UE and the second UE are in a group having a groupidentifier (ID), wherein the group ACK/NACK is associated with the groupID, and wherein the group ID is a function of grant-free resources atwhich the first grant-free uplink transmission is sent.
 18. The methodof claim 16, wherein the first UE and the second UE are in a grouphaving a group ID, wherein the group ACK/NACK is associated with thegroup ID, wherein the group ACK/NACK is received in group-commondownlink control information (DCI), and wherein a cyclic redundancycheck (CRC) of the group-common DCI is masked by the group ID.
 19. Themethod of claim 18, wherein the group ID is a function of at least oneof a time unit and frequency location at which the first grant-freeuplink transmission is sent.
 20. The method of claim 18, wherein thegroup ID is a radio network temporary identifier (RNTI) and is signaledto the first UE in radio resource control (RRC) signaling.
 21. Themethod of claim 16, wherein the group ACK/NACK message has a payloadthat indicates the ACK or NACK, wherein the payload comprises a firstbit corresponding to the first grant-free uplink transmission and asecond bit corresponding to the second grant-free uplink transmission,wherein each bit indicates whether activity detection was successful orwhether data decoding was successful.
 22. The method of claim 21,wherein a position of the first and second bits in the payloadcorresponds to at least one of an MA signature and a HARQ process ID ofthe first and second grant-free uplink transmissions.
 23. The method ofclaim 21, wherein a position of the first bit in the payload issignalled to the first UE, using radio resource control (RRC) signaling,prior to the first UE sending the first grant-free uplink transmission.24. A first user equipment (UE) comprising: a transmitter to transmit afirst grant-free uplink transmission to a base station; a receiver toreceive a group ACK/NACK message that indicates an ACK or a NACKcorresponding to the first grant-free uplink transmission and an ACK ora NACK corresponding to a second grant-free uplink transmission from asecond UE.
 25. The first UE of claim 24, wherein the first UE and thesecond UE are in a group having a group identifier (ID), wherein thegroup ACK/NACK is associated with the group ID, and wherein the group IDis a function of grant-free resources at which the first grant-freeuplink transmission is sent.
 26. The first UE of claim 24, wherein thefirst UE and the second UE are in a group having a group ID, wherein thegroup ACK/NACK is associated with the group ID, wherein the receiver isto receive the group ACK/NACK in group-common downlink controlinformation (DCI), and wherein a cyclic redundancy check (CRC) of thegroup-common DCI is masked by the group ID.
 27. The first UE of claim26, wherein the group ID is a function of at least one of a time unitand frequency location at which the first grant-free uplink transmissionis sent.
 28. The first UE of claim 24, wherein the group ACK/NACKmessage has a payload that indicates the ACK or NACK, wherein thepayload comprises a first bit corresponding to the first grant-freeuplink transmission and a second bit corresponding to the secondgrant-free uplink transmission, wherein each bit indicates whetheractivity detection was successful or whether data decoding wassuccessful.
 29. The first UE of claim 28, wherein a position of thefirst and second bits in the payload corresponds to at least one of anMA signature and a HARQ process ID of the first and second grant-freeuplink transmissions.
 30. The first UE of claim 28, wherein a positionof the first bit in the payload is signalled to the first UE, usingradio resource control (RRC) signaling, prior to the first UE sendingthe first grant-free uplink transmission.